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D - Problems with delegates

reply Paul Runde <prunde mcleodusa.net> writes:
This code works:

alias void delegate(int) t_func;

class Foo
{
   t_func func1;

   void dothis()
   {
     if (func1) func1(4); else
       printf("func1 not assigned\n");
   }

   void func(int num) { printf("num = %d\n", num); }
}

int main(char[][] args)
{
   Foo a = new Foo;
   a.dothis();
   a.func1 = &a.func;
   a.dothis();
   return 0;
}

Result:  func1 not assigned
          num = 4

However, if I move the func declaration to outside of the class, the 
line "a.func1 = &func" produces the error message:  toelem: cannot cast 
from void(*)(int num) to void delegate(int).
If I then change the t_func declaration from alias to typedef then I 
get:  cannot implicitly convert void(*)(int num) to t_func.
If I go back to the original working code and change alias to typedef 
then I get:  Internal error: e21r.c 78

What are the reasons for these error messages?  It seems to me that all 
of these senarios should work.

Thanks,

Paul
Oct 20 2002
parent "Walter" <walter digitalmars.com> writes:
Delegates are a combination of function pointer with a 'this' pointer.
Hence, a function outside of a class can't be a delegate. I'll check into
the internal error. Thanks, -Walter

"Paul Runde" <prunde mcleodusa.net> wrote in message
news:3DB37363.30709 mcleodusa.net...
 This code works:

 alias void delegate(int) t_func;

 class Foo
 {
    t_func func1;

    void dothis()
    {
      if (func1) func1(4); else
        printf("func1 not assigned\n");
    }

    void func(int num) { printf("num = %d\n", num); }
 }

 int main(char[][] args)
 {
    Foo a = new Foo;
    a.dothis();
    a.func1 = &a.func;
    a.dothis();
    return 0;
 }

 Result:  func1 not assigned
           num = 4

 However, if I move the func declaration to outside of the class, the
 line "a.func1 = &func" produces the error message:  toelem: cannot cast
 from void(*)(int num) to void delegate(int).
 If I then change the t_func declaration from alias to typedef then I
 get:  cannot implicitly convert void(*)(int num) to t_func.
 If I go back to the original working code and change alias to typedef
 then I get:  Internal error: e21r.c 78

 What are the reasons for these error messages?  It seems to me that all
 of these senarios should work.

 Thanks,

 Paul

Oct 24 2002