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digitalmars.D.learn - delegate vs function

reply spir <denis.spir gmail.com> writes:
Hello,

alias void function (int) F;
alias void delegate (int) D;

void fnFunc (F f, int i) {f(i);}
void dgFunc (D d, int i) {d(i);}

void writeOut (int i) {writeln(i);}

void test () {
    void writeIn (int i) {writeln(i);}
    fnFunc(&writeOut, 1);
    dgFunc(&writeIn, 1);
//~     fnFunc(&writeIn, 1);    // error (expected a func, got a delegate..=
.)
//~     dgFunc(&writeOut, 1);   // error (... and conversely)
}

If a function is defined at the module's toplevel and then passed (via a po=
inter) to a higher-order func that expects a function, al works fine. But i=
f it is defined inside a function, then the pointer is automatically typed =
as delegate, even if the function does not use any variable in scope, and I=
 get an error. Conversely, if the higher order func is defined to expect a =
delegate, then it fails if I pass a func defined at the top-level.
How to solve this?


Denis
-- -- -- -- -- -- --
vit esse estrany =E2=98=A3

spir.wikidot.com
Nov 23 2010
parent reply "Lars T. Kyllingstad" <public kyllingen.NOSPAMnet> writes:
On Tue, 23 Nov 2010 13:15:46 +0100, spir wrote:


 Hello,
 
 alias void function (int) F;
 alias void delegate (int) D;
 
 void fnFunc (F f, int i) {f(i);}
 void dgFunc (D d, int i) {d(i);}
 
 void writeOut (int i) {writeln(i);}
 
 void test () {
     void writeIn (int i) {writeln(i);}
     fnFunc(&writeOut, 1);
     dgFunc(&writeIn, 1);
 //~     fnFunc(&writeIn, 1);    // error (expected a func, got a
 delegate...) //~     dgFunc(&writeOut, 1);   // error (... and
 conversely) }
 
 If a function is defined at the module's toplevel and then passed (via a
 pointer) to a higher-order func that expects a function, al works fine.
 But if it is defined inside a function, then the pointer is
 automatically typed as delegate, even if the function does not use any
 variable in scope, and I get an error.


Mark the function as 'static', like this:

  static void writeIn(int i) { ... }

Then the compiler even ensures that it doesn't use any symbols from the 
enclosing scope.



 Conversely, if the higher order
 func is defined to expect a delegate, then it fails if I pass a func
 defined at the top-level. How to solve this?


Use std.functional.toDelegate(), like this:

  dgFunc(toDelegate(&writeOut), 1);

(For some reason the documentation for toDelegate() seems to be missing 
from the D web site, but I don't know why.  I'll look into it.)

-Lars
Nov 23 2010
next sibling parent "Lars T. Kyllingstad" <public kyllingen.NOSPAMnet> writes:
On Tue, 23 Nov 2010 12:25:18 +0000, Lars T. Kyllingstad wrote:


 (For some reason the documentation for toDelegate() seems to be missing
 from the D web site, but I don't know why.  I'll look into it.)


Ah, found it:
http://d.puremagic.com/issues/show_bug.cgi?id=2581

-Lars
Nov 23 2010
prev sibling parent spir <denis.spir gmail.com> writes:
On Tue, 23 Nov 2010 12:25:18 +0000 (UTC)
"Lars T. Kyllingstad" <public kyllingen.NOSPAMnet> wrote:


 On Tue, 23 Nov 2010 13:15:46 +0100, spir wrote:
=20

 Hello,
=20
 alias void function (int) F;
 alias void delegate (int) D;
=20
 void fnFunc (F f, int i) {f(i);}
 void dgFunc (D d, int i) {d(i);}
=20
 void writeOut (int i) {writeln(i);}
=20
 void test () {
     void writeIn (int i) {writeln(i);}
     fnFunc(&writeOut, 1);
     dgFunc(&writeIn, 1);
 //~     fnFunc(&writeIn, 1);    // error (expected a func, got a
 delegate...) //~     dgFunc(&writeOut, 1);   // error (... and
 conversely) }
=20
 If a function is defined at the module's toplevel and then passed (via a
 pointer) to a higher-order func that expects a function, al works fine.
 But if it is defined inside a function, then the pointer is
 automatically typed as delegate, even if the function does not use any
 variable in scope, and I get an error.


=20
 Mark the function as 'static', like this:
=20
   static void writeIn(int i) { ... }
=20
 Then the compiler even ensures that it doesn't use any symbols from the=20
 enclosing scope.


Great! that is what I have missed.


 Conversely, if the higher order
 func is defined to expect a delegate, then it fails if I pass a func
 defined at the top-level. How to solve this?


=20
 Use std.functional.toDelegate(), like this:
=20
   dgFunc(toDelegate(&writeOut), 1);


All right; if I understand, toDelegate cast a pointer to func to a delegate=
 (the pair of pointers)? (Avoiding the error.) I would enjoy this cast to b=
e automatic. So that, if we know original funcs may be of either kind, we c=
an quietly declare the parameter type as delegate.


 (For some reason the documentation for toDelegate() seems to be missing=20
 from the D web site, but I don't know why.  I'll look into it.)
=20
 -Lars





-- -- -- -- -- -- --
vit esse estrany =E2=98=A3

spir.wikidot.com
Nov 23 2010