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D - nullifying delegates

reply "Lars Ivar Igesund" <larsivi stud.ntnu.no> writes:
How do I nullify a delegate in an easy way?

I have an array of delegates and want to have
the possibility to remove some of them.

dg = null;
don't work:
cannot implicitly convert void* to void delegate(Foo)

I can take the address of a dummy static function,
but that seems silly. I guess it will work if I assign
an uninitialized delegate to it, but I really want to
use null.

Lars Ivar Igesund
Sep 20 2003
next sibling parent reply "Matthew Wilson" <matthew stlsoft.org> writes:
Does a cast (from 0 or null) not work?

"Lars Ivar Igesund" <larsivi stud.ntnu.no> wrote in message
news:bkidhp$2lpr$1 digitaldaemon.com...

 How do I nullify a delegate in an easy way?

 I have an array of delegates and want to have
 the possibility to remove some of them.

 dg = null;
 don't work:
 cannot implicitly convert void* to void delegate(Foo)

 I can take the address of a dummy static function,
 but that seems silly. I guess it will work if I assign
 an uninitialized delegate to it, but I really want to
 use null.

 Lars Ivar Igesund
Sep 20 2003
parent "Lars Ivar Igesund" <larsivi stud.ntnu.no> writes:
"Matthew Wilson" <matthew stlsoft.org> wrote in message
news:bkie1g$2me6$1 digitaldaemon.com...

 Does a cast (from 0 or null) not work?


Nope;

e2ir: cannot cast from int to void delegate(Foo)
e2ir: cannot cast from void* to void delegate(Foo)

I guess
delete dg;
might work, but it feels wrong as I don't
new
the delegate.

Another thing; how do I check if the delegate is null,
zero, empty or whatever?
Hmm, seems like !dg might work.

Lars Ivar Igesund
Sep 20 2003
prev sibling next sibling parent reply "Julio César Carrascal Urquijo" <adnoctum phreaker.net> writes:
 How do I nullify a delegate in an easy way?


This should do it:

delete dg;
Sep 20 2003
parent reply Mike Wynn <mike l8night.co.uk> writes:
Julio César Carrascal Urquijo wrote:

How do I nullify a delegate in an easy way?


 
 
 This should do it:
 
 delete dg;
 
 


I would check what you post! that will cause a seg fault, delete is for 
removing items from a hashtable/assoc array.

I tried ...
import c.stdio;
alias int delegate( int ) iid;
class foo {
	int bar(int a){ return a;}
}

int evoke( iid func ) {
	if ( func ) {
		return func( 3 );
	}
	return 0;
}

void nulldel( out iid ignore ) {
}

int main( char[][] args ) {
	iid fb;
	printf( "delegate = null (0)\n" );
	printf( "delegate != null (3)\n" );
	printf( "fb clr %d\n", evoke( fb ) );
	fb = &((new foo()).bar);
	printf( "fb set %d\n", evoke( fb ) );
	nulldel( fb );
	printf( "fb clr %d\n", evoke( fb ) );
	return evoke( fb );
}

---------------------
but has no effect!! (Walker, I assume this it a bug out should init to 
null/0)
-------------------
however ... this workaround works.
import c.stdio;
alias int delegate( int ) iid;
class foo {
	int bar(int a){ return a;}
}

int evoke( iid func ) {
	if ( func ) {
		return func( 3 );
	}
	return 0;
}

void nulldel( out iid ignore ) {
	iid fake;
	ignore = fake;
}

int main( char[][] args ) {
	iid fb;
	printf( "delegate = null (0)\n" );
	printf( "delegate != null (3)\n" );
	printf( "fb clr %d\n", evoke( fb ) );
	fb = &((new foo()).bar);
	printf( "fb set %d\n", evoke( fb ) );
	nulldel( fb );
	printf( "fb clr %d\n", evoke( fb ) );
	return evoke( fb );
}
Sep 20 2003
parent reply "Julio César Carrascal Urquijo" <adnoctum phreaker.net> writes:
I did tried that before posting using DMD 0.73 on windows. I wrote this
small program:

void main()
{
 Test t = new Test();
 void delegate(char[]) printer = &t.print;

 printer("Hello, world!\n");
 printf("printer = %p\n", printer);

 delete printer;
 printf("printer = %p\n", printer);
}


class Test
{
 void print(char[] message)
 {
  printf(message);
 }
}

That works just fine and writes:

Hello, world!
printer = 00690FD0
printer = 00000000

With no segmentation fault.



 I would check what you post! that will cause a seg fault, delete is for
 removing items from a hashtable/assoc array.


Delete is also used to delete pointers/references wich is what I did (remove
a pointer to a member function).
Sep 20 2003
parent Mike Wynn <mike l8night.co.uk> writes:
Julio César Carrascal Urquijo wrote:

 I did tried that before posting using DMD 0.73 on windows. I wrote this
 small program:
 
 void main()
 {
  Test t = new Test();
  void delegate(char[]) printer = &t.print;
 
  printer("Hello, world!\n");
  printf("printer = %p\n", printer);
 
  delete printer;
  printf("printer = %p\n", printer);
 }
 
 
 class Test
 {
  void print(char[] message)
  {
   printf(message);
  }
 }
 
 That works just fine and writes:
 
 Hello, world!
 printer = 00690FD0
 printer = 00000000
 
 With no segmentation fault.
 
 
 

I would check what you post! that will cause a seg fault, delete is for
removing items from a hashtable/assoc array.


 
 
 Delete is also used to delete pointers/references wich is what I did (remove
 a pointer to a member function).
 


but it does not do as you expect ....

import c.stdio;

class Test {
	int b;
	this() {b = 100;}
	int func(int a) {
	  printf( "test[%d]::func(%d)\n", b, a );
	  return a+b;
	}
}

alias int delegate(int) memfunc;

int main( char[][] args )
{
	int a;
	memfunc printer;
	
	if ( printer ) {
		printf("b4: printer is not null\n" );
	} else {
		printf("b4: printer is null\n" );
	}
	
	printer = &((new Test()).func);

	a = printer( 22 );
	if ( printer ) {
		printf("set: printer is not null\n" );
	} else {
		printf("set: printer is null\n" );
	}

	delete printer;
	
	if ( printer ) {
		printf("post delete: printer is not null\n" );
	} else {
		printf("post delete: printer is null\n" );
	}
	
	return 0;
}

outputs .... (linux dmd)

 b4: printer is null
 test[100]::func(22)
 set: printer is not null
 post delete: printer is not null


(I changed the delegate to int(int) 'cos the delete seggy'd when I first 
  tried it, can't get it do do that again, forgot what code I actually 
wrote).
Sep 20 2003
prev sibling next sibling parent "Walter" <walter digitalmars.com> writes:
"Lars Ivar Igesund" <larsivi stud.ntnu.no> wrote in message
news:bkidhp$2lpr$1 digitaldaemon.com...

 How do I nullify a delegate in an easy way?

 I have an array of delegates and want to have
 the possibility to remove some of them.

 dg = null;
 don't work:
 cannot implicitly convert void* to void delegate(Foo)


That should work. I'll fix it. -Walter
Sep 25 2003
prev sibling parent "Dario" <supdar yahoo.com> writes:
Lars Ivar Igesund:

 How do I nullify a delegate in an easy way?

 I have an array of delegates and want to have
 the possibility to remove some of them.

 dg = null;
 don't work:
 cannot implicitly convert void* to void delegate(Foo)


You can use "dg = dg.init" until Walter fix the bug.
Sep 25 2003