Hi,

is it possible to compare delegates?

I'm writing something like an event handling object, where i can add delegates for certain events. If i want to remove a delegate, i thought it would be the easiest way to go through may array of delegates and compare them to the one i want to remove...

Thanks,
Markus

Markus Dangl wrote:
> Hi,
> 
> is it possible to compare delegates?
> 
> I'm writing something like an event handling object, where i can add delegates for certain events. If i want to remove a delegate, i thought it would be the easiest way to go through may array of delegates and compare them to the one i want to remove...

Yes.  You can also compare delegates to (and set them to) null.

I performed a quick testcase.  The following program returned 2:

> int main() {
>   void delegate() dg = delegate void() {};
>   if(dg == delegate void() {})
>     return 1;
>    void delegate()dg2 = dg;
>   if(dg == dg2)
>     return 2;
> }

On Mon, 20 Dec 2004 07:38:23 -0700, Russ Lewis <spamhole-2001-07-16@deming-os.org> wrote:

> Markus Dangl wrote:
>> Hi,
>>  is it possible to compare delegates?
>>  I'm writing something like an event handling object, where i can add delegates for certain events. If i want to remove a delegate, i thought it would be the easiest way to go through may array of delegates and compare them to the one i want to remove...
>
> Yes.  You can also compare delegates to (and set them to) null.
>
> I performed a quick testcase.  The following program returned 2:
>
>> int main() {
>>   void delegate() dg = delegate void() {};
>>   if(dg == delegate void() {})
>>     return 1;
>>    void delegate()dg2 = dg;
>>   if(dg == dg2)
>>     return 2;
>> }
>

void delegate() dg = delegate void() {};?
There are some things the mind of mortal man is not supposed to
ken, at least not at 6.00 AM (Before, not after sleep)

But this looks very cool. Just make sure its not because you don't
provide a default return value (was it DMD that just returned eax?)

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"Unhappy Microsoft customers have a funny way of becoming Linux,
Salesforce.com and Oracle customers." - www.microsoft-watch.com:
"The Year in Review: Microsoft Opens Up"
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Simon Buchan wrote:
> void delegate() dg = delegate void() {};?
> There are some things the mind of mortal man is not supposed to
> ken, at least not at 6.00 AM (Before, not after sleep)

This actually has some practical usefulness.  Imagine that you define a delegate callback:
  void delegate() do_this_on_event_foo;
  void HandleFooEvent() {
    <do stuff here>
    do_this_on_event_foo()
  }
How do you set it to do nothing?  You have two options.  Either add a check in the above code to see if the delegate is null, or else set it to an empty delegate:
  do_this_on_event_foo = delegate void() { /* do nothing */ };
I like D!  :)



> But this looks very cool. Just make sure its not because you don't
> provide a default return value (was it DMD that just returned eax?)

d'oh!  Well, I added a 'return 0' at the end, and the executable still returns 2.

Russ Lewis schrieb:
> Markus Dangl wrote:
> 
>> Hi,
>>
>> is it possible to compare delegates?
>>
>> I'm writing something like an event handling object, where i can add delegates for certain events. If i want to remove a delegate, i thought it would be the easiest way to go through may array of delegates and compare them to the one i want to remove...
> 
> 
> Yes.  You can also compare delegates to (and set them to) null.
> 

Seems to work for me too, didn't test it though.
This is really great for identifying handlers :)

Thanks again!