Understanding behavior of member functions loaded at runtime

[Ali Çehreli via Digitalmars-d-learn]

On 03/18/2015 09:02 AM, Maeriden wrote:
> On Wednesday, 18 March 2015 at 07:57:39 UTC, Kagamin wrote:
>> You violate the ABI, try to use delegates instead of functions.
>
> I'm sorry,I don't understand what you mean.

The types that you cast to are not correct. In D, callable member 
function pointers are delegates, a type that combines a function pointer 
and a context.

import std.stdio;

struct S
{
     int a;
     int b;

     int method()
     {
         writeln(&a);
         return a + b;
     }
}

void main()
{
     auto s = S(1, 1);
     auto func = &s.method;    // <-- note lowercase s

     static assert ( is (typeof(func) == int delegate()));
     static assert (!is (typeof(func) == int function())); // <-- note !

     assert(func() == 2);
}

The function pointer and the context pointer are available through the 
.funcptr and .ptr properties of the delegate. It is possible to make a 
delegate by setting those properties:

void main()
{
     auto s = S(1, 1);

     auto func = &S.method;    // <-- note uppercase S

     static assert (!is (typeof(func) == int delegate())); // <-- note !
     static assert ( is (typeof(func) == int function()));

     int delegate() d;  // let's make a delegate
     d.funcptr = func;
     d.ptr = &s;

     assert(d() == 2);
}

Ali