LuaCOM User Manual
(Version 1.1)
Vinicius Almendra - Renato Cerqueira
LuaCOM is an add-on library to the Lua language that allows Lua
programs to use and implement objects that follow Microsoft's
Component Object Model (COM) specification and use the
ActiveX technology (or OLE automation) for property access
and method calls.
Currently, the LuaCOM library supports the following features:
- dynamic instantiation of COM objects registered in the
system registry, via the
CreateObject
method;
- dynamic access to running COM objects via
GetObject
;
- COM method calls as normal Lua function calls;
- property access as normal table field access;
- type conversion between OLE Automation types and Lua types;
- object disposal using Lua garbage collection mechanism;
- implementation of COM interfaces and objects using Lua
tables;
- use of COM connection point mechanism for bidirectional
communication and event handling;
- fully compatible with Lua 5 and with Lua 4;
- use of COM objects without type information.
Using LuaCOM is straightforward: you just have to link your program
with LuaCOM's library, include the LuaCOM's header --
luacom.h
-- and call the proper initialization and
termination functions before using any of LuaCOM's
functionalities. Here is an example of a simple C program
using LuaCOM.
/*
* Sample C program using luacom
*/
#include <stdio.h>
#include <ole2.h> // needed for OleInitialize and OleUninitialize
#include <lua.h>
#include "luacom.h"
int main (int argc, char *argv[]) {
/* COM initialization */
CoInitialize(NULL);
/* library initialization */
lua_State *L = lua_open();
luacom_open(L);
if(lua_dofile("activex_sample.lua") != 0) {
puts("Error running sample.lua!");
exit(1);
}
luacom_close(L);
lua_close(L);
CoUninitialize(NULL);
return 0;
}
Notice that it's necessary to initialize COM before
lua_open
and to terminate it only after the last
lua_close
, otherwise faults may occur.
The sample codes shown in this documentation are all for Lua 5,
although most of them should also run in Lua 4. Anyway, Lua 4 specific
samples can be found in the documentation for the previous version of
LuaCOM.
LuaCOM is composed by the following elements:
- LuaCOM API, used primarily to initialize the library,
create objects, implement ActiveX interfaces in Lua and to manipulate
connection points;
- LuaCOM objects, which make available in Lua ActiveX objects
and interfaces;
- ActiveX binding, which translates accesses on LuaCOM
objects to ActiveX interface calls and ActiveX accesses
on an interface implemented in Lua to Lua function calls or table
accesses;
- LuaCOM type conversion rules, which govern the type conversion
between Lua and ActiveX values;
- LuaCOM parameter passing rules, which describe how LuaCOM
translate a Lua parameter list to a COM one and vice versa.
The LuaCOM API is divided in two parts: the Lua API and the C/C++
API. The C/C++ API is used primarily for initialization of the
library and for low-level construction of LuaCOM objects. The Lua
API permits Lua programs to access all the functionality of
LuaCOM. All the API is accessible as functions inside a global
table named luacom
; hereafter these functions will be called
LuaCOM methods2.1. Below there is
summary of the LuaCOM API. Detailed information on these methods
is available in chapter 5.
Lua API |
|
|
CreateObject |
Creates a LuaCOM object.
|
NewObject |
Creates a LuaCOM object implemented in Lua.
|
GetObject |
Creates a LuaCOM object associated with an
instance of an already running ActiveX object.
|
ExposeObject |
Exposes a LuaCOM object, so
that other applications can get a reference to it.
|
RevokeObject |
Undoes the operation of ExposeObject.
|
RegisterObject |
Fills in the registry entries necessary for exposing a
COM object.
|
Connect |
Creates a connection point between an object and a Lua table.
|
ImplInterface |
Implements an IDispatch
interface using a Lua table.
|
ImplInterfaceFromTypelib |
Implements an
IDispatch interface described in a Type Library using a Lua table.
|
addConnection |
Connects two LuaCOM objects.
|
releaseConnection |
Disconnects a LuaCOM object from its
connection point.
|
isMember |
Checks whether a name correspond to a method
or a property of an LuaCOM object.
|
ProgIDfromCLSID |
Gets the ProgID associated with a CLSID.
|
CLSIDfromProgID |
Gets the CLSID associated with a ProgID.
|
GetIUnknown |
Returns an IUnknown interface to a LuaCOM
object as a userdata.
|
DumpTypeInfo |
Dumps to the console the type
information of the specified LuaCOM object. This method should
be used only for debugging purposes.
|
C/C++ API |
|
|
luacom_open |
Initializes the LuaCOM library in a
Lua state. It must be called before any use of LuaCOM
features.
|
luacom_close |
LuaCOM's termination function.
|
luacom_detectAutomation |
This function is a helper to create COM servers. It looks
in the command line for the switches ``/Automation'' and
``/Register'' and call some user-defined Lua functions accordingly.
|
luacom_IDispatch2LuaCOM |
Takes an IDispatch interface and creates a LuaCOM
object to expose it, pushing the object on the Lua stack.
|
LuaCOM deals with LuaCOM objects, which are no more than
a Lua table with the LuaCOM metatable and a reference to the
LuaCOM C++ object; this one is, in turn, a proxy for the ActiveX
object: it holds an IDispatch pointer to the object and translates
Lua accesses to ActiveX calls and property accesses. Here is a
sample where a LuaCOM object is used:
-- Instantiate a Microsoft(R) Calendar Object
calendar = luacom.CreateObject("MSCAL.Calendar")
-- Error check
if calendar == nil then
print("Error creating object")
exit(1)
end
-- Method call
calendar:AboutBox()
-- Property Get
current_day = calendar.Day
-- Property Put
calendar.Month = calendar.Month + 1
print(current_day)
print(calendar.Month)
LuaCOM objects can be created using the LuaCOM Lua API; there
are a number of methods that return LuaCOM objects. The most
relevant ones are CreateObject
and
GetObject
. LuaCOM objects may also be created on demand
implicitly, when a return or output value of a COM method is a
dispinterface.
LuaCOM objects are released through Lua's garbage collection
mechanism, so there isn't any explicit API method to destroy them.
A LuaCOM object may be passed as an argument to method calls on
other LuaCOM objects, if these methods expect an argument of type
dispinterface. Here is a sample to illustrate this situation:
-- Gets a running instance of Excel
excel = luacom.GetObject("Excel.Application")
-- Gets the set of worksheets
sheets = excel.Worksheets
-- gets the first two sheets
sheet1 = sheets:Item(1)
sheet2 = sheets:Item(2)
-- Exchange them (here we pass the second sheet as a parameter
-- to a method)
sheet1:Move(nil, sheet2)
There are two kinds of LuaCOM objects: typed and
generic ones. The typed ones are those whose COM object has
type information. The generic ones are those whose COM object does
not supply any type information. This distinction is important in
some situations.
The ActiveX binding is responsible for translating the table
accesses to the LuaCOM object to ActiveX interface
calls. Besides that, it also provides a mechanism for implementing
ActiveX dispinterfaces using ordinary Lua tables.
The ActiveX binding has a C++ class that implements a
generic IDispatch interface. The implementation of this class
translates the method calls and property accesses done on the objects
of this class to Lua calls and table accesses. So, one may implement
an ActiveX interface entirely in Lua provided it has a type
library describing it. This type library may be a stand-alone one
(referenced by its location on the file system) or may be associated
with some registered component. In this case, it may be referenced by
the ProgID of the component.
The C++ objects of this class can be used in any place where
an IDispatch or IUnknown interface is expected. Follows a
sample implementation of an ActiveX dispinterface in Lua.
-- Creates and fills the Lua table that will implement the
-- ActiveX interface
events_table = {}
function events_table:AfterUpdate()
print("AfterUpdate called!")
end
-- Here we implement the interface DCalendarEvents, which is part
-- of the Microsoft(R) Calendar object, whose ProgID is MSCAL.Calendar
events_obj = luacom.ImplInterface(
events_table,
"MSCAL.Calendar",
"DCalendarEvents")
-- Checks for errors
--
if events_obj == nil then
print("Implementation failed")
exit(1)
end
-- Tests the interface: this must generate a call to the events:AfterUpdate
-- defined above
--
events_obj:AfterUpdate()
If the interface to be implemented is described in a stand-alone
type library, the method ImplInterfaceFromTypelib
must be used instead:
-- Creates and fills the Lua table that will implement the
-- ActiveX interface
hello_table = {}
function hello:Hello()
print("Hello World!")
end
-- Here we implement the interface IHello
--
hello_obj = luacom.ImplInterfaceFromTypelib("hello.tlb","IHello")
-- Checks for errors
--
if hello_obj == nil then
print("Implementation failed")
os.exit(1)
end
-- Tests the interface
--
hello_obj:Hello()
Both methods return a LuaCOM object, whose corresponding ActiveX
object is implemented by the supplied table. So, any Lua calls to this LuaCOM
object will be translated to ActiveX calls which, in turn, will be translated
back to Lua calls on the implementation table. This LuaCOM object can
be passed as an argument to ActiveX methods who expect a dispinterface
or to LuaCOM API methods (like addConnection
).
One can also use the NewObject
method, which is
best suited to the situation where one needs to create a complete
ActiveX object in Lua and wants to export it, so that it can be
accessed through COM by any running application.
The ActiveX interfaces have two ``types'' of members: properties and
methods. LuaCOM deals with both.
Method accesses are done in the same way as calling Lua functions
stored in a table and having a ``self'' parameter:
obj = luacom.CreateObject("TEST.Test")
if obj == nil then
exit(1)
end
-- method call
a = obj:Teste(1,2)
-- another one
obj:Teste2(a+1)
It's important to notice the need of using the colon - ``:'' - for
method calls. Although LuaCOM does not use the self
parameter that Lua passes in this case, its presence is assumed,
that is, LuaCOM always skips the first parameter in the case of
method calls; forgetting it may cause nasty bugs.
Accessing properties is much like the same of accessing fields in
Lua tables:
obj = luacom.CreateObject("TEST.Test")
if obj == nil then
exit(1)
end
-- property access
a = obj.TestData
-- property setting
obj.TestData = a + 1
Properties may also be accessed as methods. This is mandatory when
dealing with parameterized properties, that it, ones that accept (or
demand) parameters. A common example of this situation is the ``Item''
property of collections.
-- property access
a = obj:TestData()
-- Parametrized property access
b = obj:TestInfo(2)
-- Accessing collections
c = obj.Files:Item(2)
Notice that the colon - ``:'' - must also be used in this situation.
When accessing properties with method calls, LuaCOM always
translates the method call to a read access (property get). To set the
value of a property using a method call, it's necessary append the
prefix ``set''2.2 to the property name and the new value must be
supplied as the last argument.
-- property access
a = obj:TestData()
-- Setting the property
b = obj:setTestInfo(2)
-- Setting a parametrized property
c = obj.Files:setItem(2, "test.txt")
The prefix ``get'' may also be used, to clarify the code, although
it's not necessary, as the default behavior is to make a read access.
-- property access
a = obj:getTestData()
b = obj:getTestInfo(2)
c = obj.Files:getItem(2)
To read or write properties in generic LuaCOM objects, it's
necessary access them as method calls with the right prefix
(get/set). The simpler semantic of table field access does not work
here.
obj_typ = luacom.CreateObject("Some.TypedObject")
obj_untyp = luacom.CreateObject("Untyped.Object")
-- property read (get)
a = obj_typ.Value
b = obj_untyp:getValue()
-- property write (set)
obj.typ = a + 1
obj_untyp:setValue(b + 1)
When implementing a COM
interface in Lua, LuaCOM also supports the concept of property and
of indexed properties. LuaCOM translate property reads and writes to
table field accesses:
interface = {}
interface.Test = 1
interface.TestIndex = {2,3}
obj = luacom.ImplInterface(interface, "TEST.Test", "ITest")
-- must print "1"
print(obj.Test)
-- must print nil (if there is no member named Test2)
print(obj.Test2)
-- this writes the filed Test
obj.Test = 1
-- Indexed property read. Must return 3 (remember that
-- indexed tables start at 1 in Lua)
i = obj:TestIndex(2)
-- Sets the indexed field
obj:setTestIndex(2,4)
-- Now must return 4
i = obj:TestIndex(2)
The connection points are
part of a standard ActiveX mechanism whose primary objective is to
allow the ActiveX object to notify its owner of any kind of
events. The connection point works as an ``event sink'', where
events and notifications go through.
To establish a connection using LuaCOM, the owner of the ActiveX object
must create a table to implement the connection interface,
whose description is provided by the ActiveX object (this interface
is called a source interface) and then call the API method
Connect
, passing as arguments the LuaCOM object
for the ActiveX object and the implementation table. Doing this,
LuaCOM will automatically find the default source interface, create
a LuaCOM object implemented by the supplied table and then connect
this object to the ActiveX object. Here follows a sample:
-- Creates the ActiveX object
--
calendar = luacom.CreateObject("MSCAL.Calendar")
if calendar == nil then
os.exit(1)
end
-- Creates implementation table
--
calendar_events = {}
function calendar_events:AfterUpdate()
print("Calendar updated!")
end
-- Connects object and table
--
res = luacom.Connect(calendar, calendar_events)
if res == nil then
exit(1)
end
-- This should trigger the AfterUpdate event
--
calendar:NextMonth()
It's also possible to separately create a LuaCOM object implementing the
connection point source interface and then connect it to the object using
AddConnection
.
-- Creates the ActiveX object
--
calendar = luacom.CreateObject("MSCAL.Calendar")
if calendar == nil then
print("Error instantiating calendar")
os.exit(1)
end
-- Creates implementation table
--
calendar_events = {}
function calendar_events:AfterUpdate()
print("Calendar updated!")
end
-- Creates LuaCOM object implemented by calendar_events
--
event_handler = luacom.ImplInterface(calendar_events,
"MSCAL.Calendar",
"DCalendarEvents")
if event_handler == nil then
print("Error implementing DCalendarEvents")
exit(1)
end
-- Connects both objects
--
luacom.addConnection(calendar, event_handler)
-- This should trigger the AfterUpdate event
--
calendar:NextMonth()
-- This disconnects the connection point established
--
luacom.releaseConnection(calendar)
-- This should NOT trigger the AfterUpdate event
--
calendar:NextMonth()
LuaCOM has some policies concerning parameter passing. They
specify how LuaCOM will translate COM parameter lists to Lua
and vice-versa. There are two different situations to which these
policies apply: calling a method of a COM object from Lua and
calling a Lua function from COM. The main question here is how to
deal with the different types of parameters supported by COM
(``in'' parameters, ``out'' parameters, ``in-out'' parameters,
``optional'' parameters and ``defaultvalue'' parameters). There is
also a special policy concerning generic LuaCOM objects.
This situation happens when accessing a property or calling a method
of a COM object through the LuaCOM object. Here follows a
sample:
word = luacom.GetObject("Word.Application")
-- Here we are calling the "Move" method of the Application object of
-- a running instance of Microsoft(R) Word(R)
word:Move(100,100)
In this situation, there are two steps in the parameter passing
process:
- convert Lua parameters to COM (this will be called the
``lua2com'' situation);
- convert COM's return value and output values back to
Lua (this will be called the ``com2lua'' situation).
The translation is done based on the
type information of the method (or property); it's done following the
order the parameters appear in the type information of the method. The
Lua parameters are used in the same order. For each parameter there
are three possibilities:
- The parameter is an ``in'' parameter
- LuaCOM gets the first
Lua parameter not yet converted and converts it to COM using
LuaCOM type conversion engine.
- The parameter is an ``out'' parameter
- LuaCOM ignores this
parameter, as it will only be filled by the called method. That is,
the ``out'' parameters SHOULD NOT appear in the Lua parameter list.
- The parameter is an ``in-out'' parameter
- LuaCOM does the
same as for ``in'' parameters.
When the caller of the method wants to omit a parameter, it must pass
the nil value; LuaCOM then proceeds accordingly, informing
the called method about the omission of the parameter. If the
parameter has a default value, it is used instead. Notice that
LuaCOM does not complain when one omits non-optional parameters. In
fact, LuaCOM ignores the fact that a parameter is or isn't
optional. It leaves the responsibility for checking this to the
implementation of the called method.
When the called method finishes,
LuaCOM translates the return value and the output values (that is,
the values of the ``out'' and ``in-out'' parameters) to Lua return
values. That is, the method return value is returned to the Lua code
as the first return value; the output values are returned in the order
they appear in the parameter list (notice that here we use the Lua
feature of multiple return values). If the method does not have return
values, that is, is a ``void'' method, the return values will
be the output values. If there are no output values either, then there
will be no return values.
The called method can omit the return value or the output values;
LuaCOM them will return nil for each omitted value.
To illustrate these concepts, here follows a sample of these
situations. First, we show an excerpt of an ODL file
describing a method of a COM object:
HRESULT TestShort(
[in] short p1, // an "in" parameter
[out] short* p2, // an "out" parameter
[in,out] short* p3, // an "in-out" parameter
[out,retval] short* retval); // the return value
Now follows a sample of what happens when calling the method:
-- assume that "com" is a LuaCOM object
-- Here we set p1 = 1, p3 = 2 and leave p2 uninitialized
-- When the method returns, r1 = retval and r2 = p2 and r3 = p3
r1, r2, r3 = com:TestShort(1,2)
-- WRONG! The are only two in/in-out parameters! Out parameters
-- are ignored in the lua2com parameter translation
r1, r2, r3 = com:TestShort(1,2,3) -- WRONG!
-- Here p1 = 1, p2 is uninitialized and p3 is omitted.
r1, r2, r3 = com:TestShort(1)
-- Here we ignore the output value p3
r1,r2 = com:TestShort(1)
-- Here we ignore all output values (including the return value)
com:TestShort(1,2)
When dealing with generic LuaCOM objects, the binding adopts a
different policy: all Lua parameters are converted to COM ones
as ``in-out'' parameters. If the called method sets a return value, it
is returned to Lua. As all parameters are set as ``in-out'', all of
them will be returned back to Lua, modified or not by the called
method.
This situation happens when one implements a COM dispinterface
in Lua. The ActiveX binding has to translate the COM method
calls to Lua function calls. The policy here concerning parameter
list translation is the same as the one above, just exchanging
``Lua'' for ``COM'' and vice-versa. That is, all ``in'' an
``in-out'' COM parameters are translated to parameters to the
Lua function call (the output parameters are ignored). When the
call finishes, the first return value is translated as the return
value of the COM method and the other return values are translated
as the ``in-out'' and ``out'' values, following the order they
appear in the method's type information. Continuing the previous
example, here we show the implementation of a method callable from
COM:
implementation = {}
-- This method receives TWO in/in-out parameters
function implementation:TestShort(p1, p2)
-- the first one is the retval, the second the first out param
-- the third the second out param (in fact, an in-out param)
return p1+p2, p1-p2, p1*p2
end
-- Implements an interface
obj = luacom.ImplInterface(implementation, "TEST.Test", ITest)
-- calls the function implementation:TestShort via COM
r1, r2, r3 = obj:TestShort(1,2)
COM exceptions are converted to lua_error
's containing the
data of the exception.
2.4 Type Conversion
LuaCOM is responsible for converting values from COM to Lua and
vice versa. Most of the types can be mapped from COM to Lua and vice
versa without trouble. But there are some types for which the mapping
is not obvious. LuaCOM then uses some predefined rules to do the
type conversion. These rules must be known to avoid misinterpretation
of the conversion results and to avoid errors.
2.4.1 Boolean values
LuaCOM uses the boolean values true
and false
, but
does not works with the older convention (nil
and
non-nil
; see paragraph below).
This version of Lua uses the nil value as false and
non-nil values as true. As LuaCOM gives a special meaning
for nil values in the parameter list, it can't use Lua
convention for true and false values; instead, LuaCOM uses the
C convention: the true value is a number different from zero
and the false value is the number zero. Here follows a sample:
-- This function alters the state of the of the window.
-- state is a Lua boolean value
-- window is a LuaCOM object
function showWindow(window, state)
if state then
window.Visible = 1
-- this has the same result
windows.Visible = -10
else
window.Visible = 0
end
end
-- Shows window
showWindow(window, 1)
-- Hides window
showWindow(window, nil)
A pointer to IDispatch is converted to a LuaCOMobject whose
implementation is provided by this pointer. A LuaCOMobject is
converted to COM simply passing its interface implementation to
COM.
LuaCOM just allows passing and receiving IUnknown pointers;
it does not operate on them. They are converted from/to userdatas with a
specific metatable.
LuaCOM converts Lua tables to SAFEARRAY's and
vice-versa. To be converted, Lua tables must be ``array-like'', that
is, all of its elements must be or ``scalars'' or tables of the same
length. These tables must also be ``array-like''. Here are some
samples of how is this conversion done:
Lua table |
Safe Array |
table = {"name", "phone"} |
|
table = {{1,2},{4,9}} |
|
The CURRENCY values are converted to Lua as numbers. When
converting a value to COM where a CURRENCY is expected,
LuaCOM accepts both numbers and strings formatted using the current
locale for currency values. Notice that this is highly dependent on
the configuration and LuaCOM just uses the VARIANT conversion
functions.
When converting from COM to Lua, the DATE values are
transformed in strings formatted according to the current locale. The
converse is true: LuaCOM converts strings formatted according to the
current locale to DATE values.
When LuaCOM cannot convert a value from or to COM it issues an
exception, that may be translated to a lua_error
or to a COM
exception, depending on who is the one being called.
(This chapter is under construction. Please report bugs,
mistakes or suggestions.)
With LuaCOM it is possible to implement full-fledged COM objects
using Lua. Here we understand a COM object as a composite of these
parts:
- a server, which implements one or more COM objects;
- registry information, which associates a CLSID (Class ID) to
a triple server - type library - default interface;
- a ProgID (Programmatic Identifier) which is a name associated to
a CLSID;
- a type library containing a CoClass element.
The registry information maps a ProgID to a CLSID, which is, in turn,
mapped to a server. The type information describes the component, that
is, which interfaces it exposes and what is the default interface.
LuaCOM simplifies these tasks providing some helper functions to
deal with registration and instantiation of COM servers. By now
LuaCOM supports only EXE servers, although we do not see any problem
in extending it to support DLL servers as well.
Some might argue that it would be better to implement COM object in
languages like C++ or Visual Basic©. That's true in many
situations, and false in several others. First, dealing with COM is
not easy and LuaCOM hides most its complexities; besides that, there
is another compelling reason for using LuaCOM at least in some
situations: the semantics of Lua tables and the way LuaCOM is
implemented allows one to do some neat things:
- to expose as a COM object any object that can be accessed via
Lua through a table. These might be CORBA objects, C++ objects, C
structures, Lua code etc. Using this feature, a legacy application or
library may be ``upgraded'' to COM world with little extra work;
- to use COM objects anywhere a Lua table is expected. For
example, a COM object might be ``exported'' as a CORBA object,
accessible through a network;
- to add and to redefine methods of an instance of a COM
object. This might be very useful in the preceding situations: an
object of interest might be incremented and them exported to another
client.
Of course all this flexibility comes at some cost, primarily
performance. Anyway, depending on the application, the performance
drawback might be negligible.
LuaCOM does not solve all problems: there is still the need of a
type library, which must be build using third party tools.
To avoid misunderstandings, here we'll supply the meaning we give to
some terms used in this chapter. We don't provide formal definitions:
we just want to ease the understanding of some concepts. To better
understand these concepts, see COM's documentation.
- Component
- a piece of software with some functionality that can
be used by other components. It's composed by a set of objects that
implement this functionality.
- Component Object
- an object through which all the functionality
of a component can be accessed, including its other objects. This
object may have many interfaces.
- Application Object
- A component object with a interface that
comprises all the top-level functionality of a component; the client
does not need to use other interfaces of the component object. This
concept simplifies the understanding of a component, as it puts all
its functionalities in an hierarchical manner (an application object
together with its sub-objects, which can only be accessed through
methods and properties of the application object).
- COM server
- Some piece of code that implements one or more
component objects. A COM server must tell the other applications and
components which component objects it makes available. It does so
exposing them.
- CoClass
- A type library describing a component should have a
CoClass entry, specifying some information about the component:
- a name, differentiating one CoClass from others in the same
type library;
- its CLSID, the unique identifier that distinguishes this
component from all others;
- the interfaces of the component object, telling which one is
the default. In a typical situation, only one interface will be
supplied; thus the component object could be called an Application
object for that component;
- the source interface, that is, the interface the component
uses to send events to the client. This interface is not implemented
by the component: it just uses objects that implement this
interface.
- Lua Application Object
- It's the Lua table used to implement
the Application Object.
There are some steps to build a COM server using LuaCOM:
- specify the component;
- identify what is going to be exported: Lua application object
and its sub-objects;
- build a type library for the component;
- define the registration information for the component;
- register the Component object;
- implement and expose the COM objects;
- add COM initialization and termination code.
This is the first step: to define what functionality the component
will expose. This functionality is represented by an hierarchy of
objects, rooted in the Application object. Each of these objects
should implement an interface.
Suppose we have a Lua library that implements the
access of databases contained in a specific DBMS. This library has
three types of objects: databases, queries and records. In COM world,
this could be represented by an Application object that opens
databases and returns a Database Object. A Database object has, among
others, a Query method. This method receives a SQL statement and
returns a Query object. The Query object is a collection, which can be
iterated using the parameterized property Records, which returns an
object of type Record.
The objects to be exported are those belonging to the hierarchy rooted
in the Application object. In Lua world, objects are ordinarily
represented as tables or userdatas. So it's necessary to identify (or
to implement) the Lua tables used to implement the objects to be
exported.
The type library should contain entries for all the interfaces of
exported objects and an entry for the CoClass, specifying the
interface of the Application object and the interface used to send
events.
The most common way to build a type library is to write an IDL
describing the type library and them use an IDL compiler, such as
Microsoft's© MIDL. Notice that all the interfaces must be
dispinterfaces, that is, must inherit from IDispatch, and must have
the flag oleautomation.
Here we must specify the information that is used by COM to locate the
component. See documentation of RegisterObject
.
Before being accessed by other applications, the component object must
be registered in the system registry. This can be done with the
method RegisterObject
. This task can be simplified
using the function luacom_detectAutomation
; using this function
the registration of the component can be done just running the server
with the /Register command-line switch.
Here we're dealing with COM objects implemented in Lua. Typically the
COM server will call a Lua function (like StartAutomation) to
do this task.
There are two different situations, which one demands different
actions:
- Implementing the Application Object
- Here we must use the
LuaCOM method
NewObject
to create a COM object and
bind it to the table of the Lua Application Object. Them this object must
be made available to other applications through ExposeObject
.
- Implementing other objects
- The other objects of the component
are obtained via the Lua Application Object as return values of
functions or as values stored in the fields of the Lua Application
Object (that is, via property access). These object should be
implemented using
ImplInterface
. They can be implemented
in the initialization (and then be stored somewhere) or can be
implemented on-demand (that is, each time a COM object should be
return, a call to ImplInterface
is made).
Notice that the fields of the Lua table used to implement COM
component will only be accessible if they are present in the type
library. If not, they are invisible to COM.
The COM server must call the COM initialization functions
(OleInitialize or CoInitialize) before LuaCOM is
started. Other initialization task is the implementation and
exposition of the COM objects. This task can be greatly simplified
using the C/C++ LuaCOM API function luacom_detectAutomation
.
The COM server must call (in Lua) RevokeObject
for each
exposed object. Then it must call the COM termination functions AFTER
lua_close
has been called; otherwise fatal errors may occur.
A COM server built following the preceding guidelines can be used
as any other COM object, that is, using CoCreateInstance
,
CreateObject
or something like these.
The method NewObject
returns a userdata that can be
used to send events to clients (see chapter 5 for
the reference of NewObject
).
4. Release Information
Here is provided miscellaneous information specific to the current
version of LuaCOM. Here are recorded the current limitations of
LuaCOM, its known bugs, the history of modifications since the former
version, technical details etc.
4.1 Limitations
Here are listed the current limitations of LuaCOM, as of the current
version, and information about future relaxation of this restrictions.
- LuaCOM currently supports only exposes COM objects as ``single
use'' objects. That might be circumvented by exposing many times the
same object. This restriction might be removed under request;
- the implementation of DLL server via LuaCOM isn't supported;
this may be implemented in the next release;
- LuaCOM does not use the
IEnumVARIANT
interface for
enumerations. It's necessary to use the ``Item'' field; this may be
implemented in the next release;
- there is no ``
UnRegisterObject
'' method
yet. Objects registered with RegisterObject
must be
removed from the registry manually (or using another tool); this is
due to the next release;
- LuaCOM does not support named parameters; this will be
implemented in the next version. It means that a Lua function called
from a COM application that uses named parameters may received these
not in the order they appear in the type library. This situation
happens, e.g., when using Excel© from LuaCOM and trying to
receive events;
- LuaCOM doesn't support COM methods with variable number of
parameters. This could be circumvented passing the optional parameters
inside a table, but this hasn't been tested. This may be implemented
under request;
- there isn't support for converting tables that are not
``array-like''. This may be relaxed in a future version, depending on
the feasibility;
- LuaCOM only allows one connection point for each ActiveX
object. This limitation may be relaxed in future versions;
- it's not possible to create an instance of an ActiveX object
whose initialization is done through a persistence interface
(
IPersistStream
, IPersistStorage
etc). Anyway, most of
the ActiveX objects already tested initialize themselves through
CoCreateInstance
. Initialization via persistence interfaces is
planned for a future release;
- LuaCOM doesn't provide access to COM interfaces that doesn't
inherit from IDispatch interface. That is, only Automation Objects
are supported. This restriction is due to the late-binding feature
provided by LuaCOM. It's possible to provide access to these COM
interfaces via a "proxy" Automation Object, which translate calls made
through automation to vtable (early-binding) calls. It's also possible
to implement this "proxy" directly using LuaCOM C/C++ API, but this
hasn't been tested nor tried;
- currently, almost all exceptions generate a call to
lua_error
, possibly aborting the Lua code. Where some degree
of exception handling is needed, the Lua function call
might
be used. A better exception handling mechanism might be implemented at
request.
4.2 Known bugs
Here are recorded the known bugs present in LuaCOM. If any other bugs
are found, please report them through LuaCOM's home page.
- LuaCOM only implements late-bound interfaces, but accepts a
QueryInterface for early-bound ones. This erroneous behavior is due
to the way a VB client sends events to the server. See section
4.4;
- when a table of LuaCOM objects (that is, a SAFEARRAY of
IDispatch pointers) is passed as a parameter to a COM object, these
LuaCOM objects might not be disposed automatically and may leak;
- when a COM object implemented in Lua is called from VBScript,
the ``in-out'' parameters of type SAFEARRAY cannot be modified. If
they are, VBScript will complain with a COM error.
4.3 Future Enhancements
Besides the enhancements listed in the sections 4.1 and
4.2, there are other planned enhancements:
- to improve the overall performance of LuaCOM;
- type-conversion ``metamethod'', allowing the customization of
the type conversion mechanism;
- better feedback when errors happen during the execution of
LuaCOM API methods, besides returning nil;
- dynamic creation of type libraries;
- better support for creating full-fledged COM objects using Lua.
4.4 Visual Basic© issue
A COM server implemented with LuaCOM can be used in VB with no
trouble:
Public lc as Object
Set lc = CreateObject("MyCOMObject.InLuaCOM")
lc.showWindow
b = lc.getData(3)
lc.Quit
But if one wants to received events generated by a COM object
implemented using LuaCOM, then it's necessary to use VB's
Public WithEvents
:
Public WithEvents obj as MyCOMObject.Application
Set obj = CreateObject("MyCOMObject.Application")
Private Sub obj_genericEvent()
' Put your event code here
End Sub
Here there is a problem: when VB assigns the result of
CreateObject
to obj
variable, it tries to get an early
bound interface (as far as I know, VB only uses late-bound interfaces
with variables of type Object
). LuaCOM does not work with
early-bound interfaces (known as vtable). If you call any method using
the obj
variable, VB will throw an exception.
The solution we adopted was to accept a QueryInterface for a
early-bound interface (thus allowing the use of Public
WithEvents). Then the client must do a ``typecast'' to use
correctly the COM object:
Public WithEvents obj_dummy as MyCOMObject.Application
Public obj as Object
Set obj_dummy = CreateObject("MyCOMObject.Application")
Set obj = obj_dummy
This way the client may call methods of the COM object using the
obj variable.
- LuaCOM is now compatible with Lua 4 and Lua 5. It's just a
matter of linking with the right library;
- when used with Lua 5, LuaCOM uses booleans to better match the
Automation types;
- all functions of LuaCOM's Lua API are now grouped together in a
single table called
luacom
, although they are still accessible
globally as luacom_<function> in the Lua 4 version of the
library;
- now it's possible to create instances of Microsoft©
Office© applications (Excel©, Powerpoint©
etc.). It was only possible to use them via GetObject; now you can
create a new instance of these applications using
luacom.CreateObject;
- when compiled with the NDEBUG flag, LuaCOM does not
use any kind of terminal output anymore (printf,
cout etc). This could break some applications.
- property access modified: now parameterized properties must be
accessed as functions using a prefix to differentiate property read
and write. If the prefix is omitted, a property get is assumed;
- syntax ``
obj.Property(param)
'' is no longer supported. A
colon - ``:'' - must be used: ``obj:Property(param)
'';
- better support for implementation of COM objects, including
registration and event generation;
- Type conversion engine rewritten. Now it adheres more firmly to
the types specified in the type libraries;
- binding rewritten to better support ``out'' and ``in-out''
parameters and to adhere more strictly to the recommended memory
allocation policies for COM;
- COM objects without type information are now supported.
- removal of LUACOM_TRUE and LUACOM_FALSE
constants; now booleans follow the same convention of the C language;
- memory and interface leaks fixed;
- some functions of the API have slightly different names;
- changes in memory allocation policy, to follow more strictly
practices recommended in COM documentation;
- parameter passing policies changed;
- added limited support for IUnknown pointers;
- changes in type conversion;
- added limited support for implementing and registering COM
objects in Lua
- conversion to Lua 4;
- better handling of different kinds of type information (e.g. now
can access Microsoft Internet Explorer© object);
- now handles more gracefully exceptions and errors;
- added support for optional parameters with default values;
- LuaCOM does not initializes COM libraries anymore; this is
left to the user;
- more stringent behavior about the syntax of method calls and
property access (methods with ``:'' and properties with ``.'').
5. Reference
void luacom_open(lua_State* L);
This function initializes the LuaCOM library, creates the global
luacom
table and fills it with LuaCOM methods in the given
Lua state. Notice that it's necessary to initialize COM before,
using OleInitialize or CoInitialize or something like
that.
int main()
{
lua_State *L = lua_open(0);
OleInitialize(NULL);
luacom_open(L);
.
.
.
}
void luacom_close(lua_State* L);
This function is intended to clean up the data structures associated
with LuaCOM in a specific Lua state (L). Currently, it does nothing,
but in future releases it will do. So, do not remove from your code!
It must be also called before the COM termination functions
(OleUninitialize and CoInitialize) and before
lua_close.
int main()
{
lua_State *L = lua_open(0);
OleInitialize(NULL);
luacom_open(L);
.
.
.
luacom_close(L);
lua_close(L);
OleUninitialize();
}
int luacom_detectAutomation(lua_State *L, int argc, char *argv[]);
This function gets from the top of the Lua stack a table which should
hold two fields named ``StartAutomation'' and ``Register'' (these
fields should contain functions that implement these actions). Then it
searches the command line (provided argc and argv)
for the switches ``/Automation'' or ``/Register''. If one of these
switches is found, it then calls the corresponding function in the Lua
table. Finally it returns a value telling what happened, so the caller
function may change its course of action (if needed).
This function is simply a helper for those implementing Automation
servers using LuaCOM. Most of the work should be done by the Lua
code, using the methods RegisterObject
,
NewObject
, and ExposeObject
.
/*
* com_object.cpp
*
* This sample C++ code initializes the libraries and
* the COM engine to export a COM object implemented in Lua
*/
#include <ole2.h>
// libraries
extern "C"
{
#include <lua.h>
#include <lualib.h>
}
#include <luacom.h>
int main (int argc, char *argv[])
{
int a = 0;
CoInitialize(NULL);
IupOpen();
lua_State *L = lua_open(0);
lua_baselibopen (L);
lua_strlibopen(L);
lua_iolibopen(L);
luacom_open(L);
lua_dofile(L, "implementation.lua");
// Pushes the table containing the functions
// responsible for the initialization of the
// COM object
lua_getglobal(L, "COM");
// detects whether the program was invoked for Automation,
// registration or none of that
int result = luacom_detectAutomation(L, argc, argv);
switch(result)
{
case LUACOM_AUTOMATION:
// runs the message loop, as all the needed initialization
// has already been performed
MessageLoop();
break;
case LUACOM_NOAUTOMATION:
// This only works as a COM server
printf("Error. This is a COM server\n");
break;
case LUACOM_REGISTER:
// Notifies that the COM object has been
// registered
printf("COM object successfully registered.");
break;
case LUACOM_AUTOMATION_ERROR:
// detectAutomation found /Automation or /Register but
// the initialization Lua functions returned some error
printf("Error starting Automation");
break;
}
luacom_close(L);
lua_close(L);
CoUninitialize();
return 0;
}
-------
-- implementation.lua
--
-- This is a sample implementation of a COM server in Lua
--
-- This is the implementation of the COM object
TestObj = {}
function TestObj:showWindow()
dialog.show()
end
function TestObj:hideWindow()
dialog.hide()
end
-- Here we create and populate the table to
-- be used with detectAutomation
COM = {}
-- This functions creates the COM object to be
-- exported and exposes it.
function COM:StartAutomation()
-- creates the object using its default interface
COMAppObject, events, e = luacom.NewObject(TestObj, "TESTE.Teste")
-- This error will be caught by detectAutomation
if COMAppObject == nil then
error("NewObject failed: "..e)
end
-- Exposes the object
cookie = luacom.ExposeObject(COMAppObject)
if cookie == nil then
error("ExposeObject failed!")
end
end
function COM:Register()
-- fills table with registration information
local reginfo = {}
reginfo.VersionIndependentProgID = "TESTE.Teste"
reginfo.ProgID = reginfo.VersionIndependentProgID..".1"
reginfo.TypeLib = "teste.tlb"
reginfo.CoClass = "Teste"
reginfo.ComponentName = "Test Component"
reginfo.Arguments = "/Automation"
-- stores component information in the registry
local res = luacom.RegisterObject(reginfo)
if res == nil then
error("RegisterObject failed!")
end
end
int luacom_IDispatch2LuaCOM(lua_State *L, void *pdisp_arg);
This functions takes a pointer to IDispatch, creates a
LuaCOM object for it and pushes it in the Lua stack. This function
is useful when one gets an interface for a COM object from
C/C++ code and wants to use it in Lua.
void CreateAndExport(lua_State* L)
{
// Creates the object
IUnknown *obj = CreateObj();
// Gets the IDispatch
IDispatch* pdisp = NULL;
QueryInterface(IID_IDISPATCH, &pdisp);
// pushes onto lua stack
luacom_IDispatch2LuaCOM(L, (void *) pdisp);
}
luacom_obj = luacom.CreateObject(ProgID)
This method finds the Class ID referenced by the ProgID parameter
and creates an instance of the object with this Class ID. If there
is any problem (ProgID not found, error instantiating object), the
method returns nil.
Parameter |
Type |
ProgID |
String |
Return Item |
Possible Values |
luacom_obj |
LuaCOM object
nil |
inet_obj = luacom.CreateObject("InetCtls.Inet")
if inet_obj == nil then
print("Error! Object could not be created!")
end
implemented_obj = luacom.Connect(luacom_obj, implementation_table)
This method finds the default source interface of the object
luacom_obj
, creates an instance of this interface whose
implementation is given by implementation_table
and creates a
connection point between the luacom_obj
and the implemented
source interface. Any calls made by the luacom_obj
to the
source interface implementation will be translated to Lua calls to
member function present in the implementation_table
. If the
method succeeds, the LuaCOM object implemented by
implementation_table
is returned; otherwise, nil
is
returned.
Parameter |
Type |
luacom_obj |
LuaCOM object |
implementation_table |
Table or userdata |
Return Item |
Possible Values |
implemented_obj |
LuaCOM object
nil |
events_handler = {}
function events_handler:NewValue(new_value)
print(new_value)
end
events_obj = luacom.Connect(luacom_obj, events_handler)
implemented_obj = luacom.ImplInterface(impl_table, ProgID, interface_name)
This method finds the type library associated with the ProgID and
tries to find the type information of an interface called
``interface_name''. If it does, then creates an object whose
implementation is ``impl_table'', that is, any method call or property
access on this object is translated to calls or access on the members
of the table. Then it makes a LuaCOM object for the implemented
interface and returns it. If there are any problems in the process
(ProgID not found, interface not found, interface isn't a
dispinterface), the method returns nil.
Parameter |
Type |
impl_table |
table or userdata |
ProgID |
string |
interface_name |
string |
Return Item |
Possible Values |
implemented_obj |
LuaCOM object
nil |
myobject = {}
function myobject:MyMethod()
print("My method!")
end
myobject.Property = "teste"
luacom_obj = luacom.ImplInterface(myobject, "TEST.Test", "ITest")
-- these are done via Lua
myobject:MyMethod()
print(myobject.Property)
-- this call is done through COM
luacom_obj:MyMethod()
print(luacom_obj.Property)
impl_obj = luacom.ImplInterfaceFromTypelib(
impl_table,
typelib_path,
interface_name,
coclass_name)
This method loads the type library whose file path is
``typelib_path'' and tries to find the type information of an
interface called ``interface_name''. If it does, then creates an
object whose implementation is ``impl_table'', that is, any method
call or property access on this object is translated to calls or
access on the members of the table. Then it makes a LuaCOM object
for the implemented interface and returns it. If there are any
problems in the process (ProgID not found, interface not found,
interface isn't a dispinterface), the method returns nil. The
``coclass_name'' parameter is optional; it is only needed if the
resulting LuaCOM object is to be passed to the methods
Connect
, AddConnection
or
ExposeObject
. This parameter specifies the Component
Object class name to which the interface belongs, as one interface may
be used in more than one ``coclass''.
Parameter |
Type |
impl_table |
table or userdata |
typelib_path |
string |
interface_name |
string |
coclass_name |
(optional) string |
Return Item |
Possible Values |
implemented_obj |
LuaCOM object
nil |
myobject = {}
function myobject:MyMethod()
print("My method!")
end
myobject.Property = "teste"
luacom_obj = luacom.ImplInterfaceFromTypelib(myobject, "test.tlb",
"ITest", "Test")
-- these are done via Lua
myobject:MyMethod()
print(myobject.Property)
-- this call is done through COM
luacom_obj:MyMethod()
print(luacom_obj.Property)
luacom_obj = luacom.GetObject(ProgID)
This method finds the Class ID referenced by the ProgID parameter
and tries to find a running instance of the object having this Class
ID. If there is any problem (ProgID not found, object is not running),
the method returns nil.
Parameter |
Type |
ProgID |
String |
Return Item |
Possible Values |
luacom_obj |
LuaCOM object
nil |
excel = luacom.GetObject("Excel.Application")
if excel == nil then
print("Error! Could not get object!")
end
implemented_obj, events_sink, errmsg = luacom.NewObject(impl_table, ProgID)
This method is analogous to ImplInterface
, doing
just a step further: it locates the default interface for the ProgID
and uses its type information. That is, this method creates a Lua
implementation of a COM object's default interface. This is useful
when implementing a complete COM object in Lua. It also creates a
connection point for sending events to the client application and
returns it as the second return value. If there are any problems in
the process (ProgID not found, default interface is not a
dispinterface etc), the method returns nil twice and returns the
error message as the third return value.
To send events to the client application, just call methods of the
event sink table returned. The method call will be translated to COM
calls to each connection. These calls may contain parameters (as
specified in the type information).
Parameter |
Type |
impl_table |
table or userdata |
ProgID |
string |
Return Item |
Possible Values |
implemented_obj |
LuaCOM object
nil |
event_sink |
event sink table
nil |
errmsg |
error message in the case of failure
nil |
myobject = {}
function myobject:MyMethod()
print("My method!")
end
myobject.Property = "teste"
obj, evt, err = luacom.NewObject(myobject, "TEST.Test")
-- these are done via Lua
myobject:MyMethod()
print(myobject.Property)
-- this call is done through COM
luacom_obj:MyMethod()
print(luacom_obj.Property)
-- here we sink events
evt:Event1()
cookie = luacom.ExposeObject(luacom_obj)
This method creates and registers a class factory for
luacom_obj, so that other running applications can use it. It
returns a cookie that must be used to unregister the object. If the
method fails, it returns nil.
ATTENTION: the object MUST be unregistered (using
RevokeObject
) before calling luacom_close or
lua_close, otherwise unhandled exceptions might occur.
Parameter |
Type |
luacom_obj |
LuaCOM object |
Return Item |
Possible Values |
cookie |
number
nil |
myobject = luacom.NewObject(impl_table, "Word.Application")
cookie = luacom.ExposeObject(myobject)
function end_of_application()
luacom.RevokeObject(cookie)
end
result = luacom.RegisterObject(registration_info)
This method creates the necessary registry entries for a COM object,
using the information in registration_info table. If the
component is successfully registered, the method returns a non-nil
value.
The registration_info table must contain the following
fields5.1:
- VersionIndependentProgID
- This field must contain a string
describing the programmatic identifier for the component,
e.g. ``MyCompany.MyApplication''.
- ProgID
- The same as VersionIndependentProgID but with a version
number, e.g. ``MyCompany.MyApplication.2''.
- TypeLib
- The file name of the type library describing the
component. This file name should contain a path, if the type library
isn't in the same folder of the executable. Samples:
mytypelib.tlb
, c:\app\test.tlb
, test.exe\1
(this
last one can be used when the type library is bound to the executable
as a resource).
- CoClass
- The name of the component class. There must be a
coclass entry in the type library with the same name or the
registration will fail.
- ComponentName
- This is the human-readable name of the
component.
- Arguments
- This field specifies what arguments will be supplied
to the component executable when started via COM. Normally it should
contain ``/Automation''.
This method is not a generic ``registering tool'' for COM
components, as it assumes the component to be registered is
implemented by the running executable during registration.
Parameter |
Type |
registration_info |
table with registration information |
Return Item |
Possible Values |
result |
nil or non-nil value |
-- Lua registration code
function RegisterComponent()
reginfo.VersionIndependentProgID = "TESTE.Teste"
-- Adds version information
reginfo.ProgID = reginfo.VersionIndependentProgID..".1"
reginfo.TypeLib = "teste.tlb"
reginfo.CoClass = "Teste"
reginfo.ComponentName = "Test Component"
reginfo.Arguments = "/Automation"
local res = luacom.RegisterObject(reginfo)
return res
end
result = luacom.addConnection(client, server)
This method connects two LuaCOM objects, setting the
server as an event sink for the client, that is, the
client will call methods of the server to notify events (following the
COM model). This will only work if the client supports
connection points of the server's type. If the method
succeeds, it returns 1; otherwise, it returns nil.
Parameter |
Type |
client |
LuaCOM object |
server |
LuaCOM object |
Return Item |
Possible Values |
result |
number
nil |
obj = luacom.CreateObject("TEST.Test")
event_sink = {}
function event_sink:KeyPress(keynumber)
print(keynumber)
end
event_obj = luacom.ImplInterface(
event_sink, "TEST.Test", "ITestEvents")
result = luacom.addConnection(obj, event_obj)
if result == nil then
print("Error!")
exit(1)
end
luacom.releaseConnection(client)
This method disconnects a LuaCOM object from its event sink.
Parameter |
Type |
client |
LuaCOM object |
There are none.
obj = luacom.CreateObject("TEST.Test")
event_sink = {}
function event_sink:KeyPress(keynumber)
print(keynumber)
end
event_obj = luacom.ImplInterface(
event_sink, "TEST.Test", "ITestEvents")
result = luacom.addConnection(obj, event_obj)
if result == nil then
print("Error!")
exit(1)
end
.
.
.
luacom.releaseConnection(obj)
progID = luacom.ProgIDfromCLSID(clsid)
This method is a proxy for the Win32 function ProgIDFromCLSID.
Parameter |
Type |
clsid |
string |
Return Item |
Possible Values |
progID |
string
nil |
progid = luacom.ProgIDfromCLSID("{8E27C92B-1264-101C-8A2F-040224009C02}")
obj = luacom.CreateObject(progid)
clsid = luacom.CLSIDfromProgID(progID)
It's the inverse of ProgIDfromCLSID
.
luacom.ShowHelp(luacom_obj)
This method tries to locate the luacom_obj's help file in its
type information and shows it.
Parameter |
Type |
luacom_obj |
LuaCOM object |
None.
obj = luacom.CreateObject("TEST.Test")
luacom.ShowHelp(obj)
iunknown = luacom.GetIUnknown(luacom_obj)
This method returns a userdata holding the IUnknown interface
pointer to the COM object behind luacom_obj. It's important
to notice that Lua does not duplicates userdata: many calls to
GetIUnknown
for the same LuaCOM object will return
the same userdata. This means that the reference count for the
IUnknown interface will be incremented only once (that is, the
first time the userdata is pushed) and will be decremented only when
all the references to that userdata go out of scope (that is, when the
userdata suffers garbage collection).
One possible use for this method is to check whether two LuaCOM
objects reference the same COM object.
Parameter |
Type |
luacom_obj |
LuaCOM object |
Return Item |
Possible Values |
iunknown |
userdata with IUnknown metatable
nil |
-- Creates two LuaCOM objects for the same COM object
-- (a running instance of Microsoft Word(R) )
word1 = luacom.GetObject("Word.Application")
word2 = luacom.GetObject("Word.Application")
-- These two userdata should be the same
unk1 = luacom.GetIUnknown(word1)
unk2 = luacom.GetIUnknown(word2)
assert(unk1 == unk2)
answer = luacom.isMember(luacom_obj, member_name)
This method returns true (that is, different from nil) if
there exists a method or a property of the luacom_obj named
member_name.
Parameter |
Type |
luacom_obj |
LuaCOM object |
member_name |
string |
Return Item |
Possible Values |
answer |
nil or non-nil |
obj = luacom.CreateObject("MyObject.Test")
if luacom.isMember(obj, "Test") then
result = obj:Test()
end
LuaCOM has been developed by Renato Cerqueira and Vinicius
Almendra. The project has been sponsored by TeCGraf (Technology Group
on Computer Graphics).
LuaCOM User Manual
(Version 1.1)
This document was generated using the
LaTeX2HTML translator Version 2K.1beta (1.47)
Copyright © 1993, 1994, 1995, 1996,
Nikos Drakos,
Computer Based Learning Unit, University of Leeds.
Copyright © 1997, 1998, 1999,
Ross Moore,
Mathematics Department, Macquarie University, Sydney.
The command line arguments were:
latex2html -dir luacom-htmldoc -split 0 -show_section_numbers -local_icons -no_navigation -numbered_footnotes luacom.tex
The translation was initiated by Vinicius da Silva Almendra on 2003-06-27
Footnotes
- ...methods2.1
- In version 1.1 the old API is still
accessible when LuaCOM is used with Lua 4, so that code written
for LuaCOM 1.0 still works with LuaCOM 1.1. It means that all
functions of the API can be accessed as luacom_<function>
or as luacom.<function>. This may change in the next
versions, so upgrade your code as soon as possible!
- ... ``set''2.2
- In a future version it might be allowed to
change the prefix.
- ...
fields5.1
- For a better description of these fields, see COM's
documentation.
Vinicius da Silva Almendra
2003-06-27