[fpc-pascal] how to use procedure of object in C

[Michael Van Canneyt]

On Mon, 9 Mar 2015, OBones wrote:

> Michael Van Canneyt wrote:
>> 
>> 
>> On Mon, 9 Mar 2015, Xiangrong Fang wrote:
>> 
>>> Hi all,
>>> I define a procedure like this:
>>> 
>>> type
>>>   TDataHandler = procedure(data: Pointer) of object;
>>> 
>>> procedure SetHandler(h: TDataHandler); external cdecl;
>>> 
>>> Now, can I implement SetHandler in a library written in C, then call h in 
>>> C?
>> 
>> IMHO Not without separate assembler code for each CPU.
>> 
>> Michael.
> How about using TMethod?
>
> procedure DataHandler(DummySelf: Pointer; data: Pointer);
> begin
>  // do what you want to do, DummySelf is always nil.
> end;
>
> var
>  Method: TMethod;
> begin
>  Method.Data := nil;
>  Method.Code := @DataHandler;
>
>  SetHandler(TDataHandler(Method));
> end;

You must be sure that self is passed in the correct register.
I am not sure this is the case if you declare it as an extra argument.
It may be so, but compiler people should confirm this. 
I don't think you can take it for granted.

Michael.