Is it possible to create a template which only accepts functions or delegates like this example:

class Example(T : void function()) { // or ..(T : void delegate())..

	T callback;

}

Where T is a function or a delegate...

Thanks for every suggestion!

On Wed, 09 Feb 2011 14:35:42 -0500, useo <useo@start.bg> wrote:

> Is it possible to create a template which only accepts functions or
> delegates like this example:
>
> class Example(T : void function()) { // or ..(T : void delegate())..
>
> 	T callback;
>
> }
>
> Where T is a function or a delegate...
>
> Thanks for every suggestion!

class Example(T) if (is(T == delegate) || is(T == function))
{
    T callback;
}

-Steve

== Auszug aus Steven Schveighoffer (schveiguy@yahoo.com)'s Artikel
> On Wed, 09 Feb 2011 14:35:42 -0500, useo <useo@start.bg> wrote:
> > Is it possible to create a template which only accepts functions
or
> > delegates like this example:
> >
> > class Example(T : void function()) { // or ..(T : void delegate
())..
> >
> > 	T callback;
> >
> > }
> >
> > Where T is a function or a delegate...
> >
> > Thanks for every suggestion!
> class Example(T) if (is(T == delegate) || is(T == function))
> {
>      T callback;
> }
> -Steve

Wow, works great - THANKS :)

== Auszug aus Steven Schveighoffer (schveiguy@yahoo.com)'s Artikel
> On Wed, 09 Feb 2011 14:35:42 -0500, useo <useo@start.bg> wrote:
> > Is it possible to create a template which only accepts functions
or
> > delegates like this example:
> >
> > class Example(T : void function()) { // or ..(T : void delegate
())..
> >
> > 	T callback;
> >
> > }
> >
> > Where T is a function or a delegate...
> >
> > Thanks for every suggestion!
> class Example(T) if (is(T == delegate) || is(T == function))
> {
>      T callback;
> }
> -Steve

Is there any chance to do the same for methods like:

void example(T)() {
}

... something like:

void bindEvent(T)(if (is(T == delegate) || is(T == function)))()...

On Wed, 09 Feb 2011 14:59:33 -0500, useo <useo@start.bg> wrote:

> == Auszug aus Steven Schveighoffer (schveiguy@yahoo.com)'s Artikel
>> On Wed, 09 Feb 2011 14:35:42 -0500, useo <useo@start.bg> wrote:
>> > Is it possible to create a template which only accepts functions
> or
>> > delegates like this example:
>> >
>> > class Example(T : void function()) { // or ..(T : void delegate
> ())..
>> >
>> > 	T callback;
>> >
>> > }
>> >
>> > Where T is a function or a delegate...
>> >
>> > Thanks for every suggestion!
>> class Example(T) if (is(T == delegate) || is(T == function))
>> {
>>      T callback;
>> }
>> -Steve
>
> Is there any chance to do the same for methods like:
>
> void example(T)() {
> }
>
> ... something like:
>
> void bindEvent(T)(if (is(T == delegate) || is(T == function)))()...

Yes, but you have the order mixed up.

void bindEvent(T)() if (is...)

In general form, a template constraint goes after the declaration, but before the body of the template.

-Steve

useo:

> ... something like:
> 
> void bindEvent(T)(if (is(T == delegate) || is(T == function)))()...

void foo(T)(T x) if (is(T == delegate) || is(T == function)) { ... }

Bye,
bearophile

== Auszug aus Steven Schveighoffer (schveiguy@yahoo.com)'s Artikel
> On Wed, 09 Feb 2011 14:59:33 -0500, useo <useo@start.bg> wrote:
> > == Auszug aus Steven Schveighoffer (schveiguy@yahoo.com)'s Artikel
> >> On Wed, 09 Feb 2011 14:35:42 -0500, useo <useo@start.bg> wrote:
> >> > Is it possible to create a template which only accepts
functions
> > or
> >> > delegates like this example:
> >> >
> >> > class Example(T : void function()) { // or ..(T : void delegate
> > ())..
> >> >
> >> > 	T callback;
> >> >
> >> > }
> >> >
> >> > Where T is a function or a delegate...
> >> >
> >> > Thanks for every suggestion!
> >> class Example(T) if (is(T == delegate) || is(T == function))
> >> {
> >>      T callback;
> >> }
> >> -Steve
> >
> > Is there any chance to do the same for methods like:
> >
> > void example(T)() {
> > }
> >
> > ... something like:
> >
> > void bindEvent(T)(if (is(T == delegate) || is(T == function)))
()...
> Yes, but you have the order mixed up.
> void bindEvent(T)() if (is...)
> In general form, a template constraint goes after the declaration,
but
> before the body of the template.
> -Steve

Ah, okay... I already tried the if-statement after the declaration but I always got an error like this:

"... semicolon expected following function declaration"

I just removed ( and ) from the if-statement and it's working, thanks
in again!

I just have a problem with my variables.

For example... my class/template just looks like:

class Example(T) if (is(T == delegate) || is(T == function))
{
   T callback;

   void setCallback(T cb) {
      callback = cb;
   }

}

This means that I need variables like Example!(void function()) myVariable. But is there any possibility to use variables like Example myVariable? The template declaration only defines the type of a callback and perhaps one method-declaration nothing else. I already tried Example!(void*) because delegates and functions are void pointers but I always get an error. I hope there is any way to do this.

On Wed, 09 Feb 2011 16:14:04 -0500, useo <useo@start.bg> wrote:

> I just have a problem with my variables.
>
> For example... my class/template just looks like:
>
> class Example(T) if (is(T == delegate) || is(T == function))
> {
>    T callback;
>
>    void setCallback(T cb) {
>       callback = cb;
>    }
>
> }
>
> This means that I need variables like Example!(void function())
> myVariable. But is there any possibility to use variables like
> Example myVariable? The template declaration only defines the type of
> a callback and perhaps one method-declaration nothing else. I already
> tried Example!(void*) because delegates and functions are void
> pointers but I always get an error. I hope there is any way to do
> this.

If I understand you correctly, you don't want to declare the type of T when instantiating the template?  This is not possible, templates must have all parameters defined at instantiation time.

If you just want a shorter thing to type for Example!(void function()), you can do:

alias Example!(void function()) MyType;

MyType myVariable;

-Steve

useo:

> I just have a problem with my variables.
> 
> For example... my class/template just looks like:
> 
> class Example(T) if (is(T == delegate) || is(T == function))
> {
>    T callback;
> 
>    void setCallback(T cb) {
>       callback = cb;
>    }
> 
> }
> 
> This means that I need variables like Example!(void function())
> myVariable. But is there any possibility to use variables like
> Example myVariable?

D is not the SML language, templates are just placeholders. If you don't instantiate a template, you have only a symbol. Example is only assignable to an alias (and in past, to a typedef):
alias Example Foo;


> The template declaration only defines the type of
> a callback and perhaps one method-declaration nothing else. I already
> tried Example!(void*) because delegates and functions are void
> pointers but I always get an error. I hope there is any way to do
> this.

I don't yet understand what you are trying to do.

Other notes:
- What if your T is a functor (a callable class/struct/union instance that defined opCall)?
- sizeof of a function pointer is 1 CPU word, while a delegate is 2 CPU words (and a delegate clojure has stuff on the heap too, sometimes).

Bye,
bearophile