delegate vs function

[spir]

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. 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
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spir.wikidot.com

Re: delegate vs function

[Lars T. Kyllingstad]

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

Re: delegate vs function

[Lars T. Kyllingstad]

On Tue, 23 Nov 2010 12:25:18 +, 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

Re: delegate vs function

[spir]

On Tue, 23 Nov 2010 12:25:18 + (UTC)
Lars T. Kyllingstad pub...@kyllingen.nospamnet wrote:

 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.

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?
 
 Use std.functional.toDelegate(), like this:
 
   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 be 
automatic. So that, if we know original funcs may be of either kind, we can 
quietly declare the parameter type as delegate.

 (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




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vit esse estrany ☣

spir.wikidot.com