Code:

// Converting method pointers into function pointers

// Often you need a function pointer for a callback function. But what, if you want to specify a method as

// an callback? Converting a method pointer to a function pointer is not a trivial task; both types are

// incompatible with each other. Although you have the possibility to convert like this "@TClass.SomeMethod",

// this is more a hack than a solution, because it restricts the use of this method to some kind of a class

// function, where you cannot access instance variables. If you fail to do so, you'll get a wonderful gpf.

// But there is a better solution: run time code generation! Just allocate an executable memory block, and

// write 4 machine code instructions into it: 2 instructions loads the two pointers of the method pointer

// (code & data) into the registers, one calls the method via the code pointer, and the last is just a return

// Now you can use this pointer to the allocated memory as a plain function pointer, but in fact you are

// calling a method for a specific instance of a Class.

type TMyMethod = procedureofobject;

function MakeProcInstance(M: TMethod): Pointer;

begin

// allocate memory

GetMem(Result, 15);

asm

// MOV ECX,

MOV BYTE PTR [EAX], $B9

MOV ECX, M.Data

MOV DWORD PTR [EAX+$1], ECX

// POP EDX

MOV BYTE PTR [EAX+$5], $5A

// PUSH ECX

MOV BYTE PTR [EAX+$6], $51

// PUSH EDX

MOV BYTE PTR [EAX+$7], $52

// MOV ECX,

MOV BYTE PTR [EAX+$8], $B9

MOV ECX, M.Code

MOV DWORD PTR [EAX+$9], ECX

// JMP ECX

MOV BYTE PTR [EAX+$D], $FF

MOV BYTE PTR [EAX+$E], $E1

end;

end;

procedure FreeProcInstance(ProcInstance: Pointer);

begin

// free memory

FreeMem(ProcInstance, 15);

end;