www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Template for function or delegate (nothing else)

reply useo <useo start.bg> writes:
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!
Feb 09 2011
parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
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
Feb 09 2011
next sibling parent useo <useo start.bg> writes:
== 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 :)
Feb 09 2011
prev sibling parent reply useo <useo start.bg> writes:
== 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)))()...
Feb 09 2011
next sibling parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
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
Feb 09 2011
parent reply useo <useo start.bg> writes:
== 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!
Feb 09 2011
parent reply useo <useo start.bg> writes:
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.
Feb 09 2011
next sibling parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
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
Feb 09 2011
parent useo <useo start.bg> writes:
== Auszug aus Steven Schveighoffer (schveiguy yahoo.com)'s Artikel

 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


Yes, right, I don't want declare the template-type.

Nevertheless... thanks
Feb 09 2011
prev sibling parent reply bearophile <bearophileHUGS lycos.com> writes:
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
Feb 09 2011
parent reply useo <useo start.bg> writes:
== Auszug aus bearophile (bearophileHUGS lycos.com)'s Artikel

 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


Idea is the following:

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

   T callback;

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

   void opCall() {
      callback();
   }

}

other file:

import example;

private {

   Example variable;

}

void setExampleVariable(Example ex) {
   variable = ex;
}

void callCurrentExampleVariable() {
   variable();
}
Feb 09 2011
parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Wed, 09 Feb 2011 16:41:25 -0500, useo <useo start.bg> wrote:


 == Auszug aus bearophile (bearophileHUGS lycos.com)'s Artikel

 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


 Idea is the following:

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

    T callback;

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

    void opCall() {
       callback();
    }

 }

 other file:

 import example;

 private {

    Example variable;

 }

 void setExampleVariable(Example ex) {
    variable = ex;
 }

 void callCurrentExampleVariable() {
    variable();
 }


I don't think you want templates.  What you want is a tagged union (and a  
struct is MUCH better suited for this):

// untested!

struct Example
{
    private
    {
       bool isDelegate;
       union
       {
          void function() fn;
          void delegate() dg;
       }
    }

    void setCallback(void function() f) { this.fn = f; isDelegate = false;}
    void setCallback(void delegate() d) { this.dg = d; isDelegate = true;}

    void opCall()
    {
       if(isDelegate)
          dg();
       else
          fn();
    }
}

-Steve
Feb 09 2011
next sibling parent useo <useo start.bg> writes:
== Auszug aus Steven Schveighoffer (schveiguy yahoo.com)'s Artikel

 On Wed, 09 Feb 2011 16:41:25 -0500, useo <useo start.bg> wrote:

 == Auszug aus bearophile (bearophileHUGS lycos.com)'s Artikel

 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


 Idea is the following:

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

    T callback;

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

    void opCall() {
       callback();
    }

 }

 other file:

 import example;

 private {

    Example variable;

 }

 void setExampleVariable(Example ex) {
    variable = ex;
 }

 void callCurrentExampleVariable() {
    variable();
 }


 I don't think you want templates.  What you want is a tagged


union (and a

 struct is MUCH better suited for this):
 // untested!
 struct Example
 {
     private
     {
        bool isDelegate;
        union
        {
           void function() fn;
           void delegate() dg;
        }
     }
     void setCallback(void function() f) { this.fn = f;


isDelegate = false;}

     void setCallback(void delegate() d) { this.dg = d;


isDelegate = true;}

     void opCall()
     {
        if(isDelegate)
           dg();
        else
           fn();
     }
 }
 -Steve


Looks really interesting and seems to work. Thanks in advance!
Feb 09 2011
prev sibling parent reply spir <denis.spir gmail.com> writes:
On 02/09/2011 11:05 PM, Steven Schveighoffer wrote:

 On Wed, 09 Feb 2011 16:41:25 -0500, useo <useo start.bg> wrote:


 == Auszug aus bearophile (bearophileHUGS lycos.com)'s Artikel

 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


 Idea is the following:

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

 T callback;

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

 void opCall() {
 callback();
 }

 }

 other file:

 import example;

 private {

 Example variable;

 }

 void setExampleVariable(Example ex) {
 variable = ex;
 }

 void callCurrentExampleVariable() {
 variable();
 }


 I don't think you want templates. What you want is a tagged union (and a struct
 is MUCH better suited for this):

 // untested!

 struct Example
 {
 private
 {
 bool isDelegate;
 union
 {
 void function() fn;
 void delegate() dg;
 }
 }

 void setCallback(void function() f) { this.fn = f; isDelegate = false;}
 void setCallback(void delegate() d) { this.dg = d; isDelegate = true;}

 void opCall()
 {
 if(isDelegate)
 dg();
 else
 fn();
 }
 }


Waow, very nice solution.
I really question the function/delegate distinction (mostly artificial, imo) 
that "invents" issues necessiting workarounds like that. What does it mean, 
what does it bring?
Right, there is one pointer less for funcs. This save 4 or 8 bytes, so to say, 
nothing; who develops apps with arrays of billions of funcs? There are written 
in source ;-) Even then, if this saving of apointer was of any relevance, then 
it should be an implementation detail that does not leak into artificial 
semantic diff, creating issues on the programmer side. What do you think?

Denis
-- 
_________________
vita es estrany
spir.wikidot.com
Feb 10 2011
parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Thu, 10 Feb 2011 08:39:13 -0500, spir <denis.spir gmail.com> wrote:


 On 02/09/2011 11:05 PM, Steven Schveighoffer wrote:



 I don't think you want templates. What you want is a tagged union (and  
 a struct
 is MUCH better suited for this):

 // untested!

 struct Example
 {
 private
 {
 bool isDelegate;
 union
 {
 void function() fn;
 void delegate() dg;
 }
 }

 void setCallback(void function() f) { this.fn = f; isDelegate = false;}
 void setCallback(void delegate() d) { this.dg = d; isDelegate = true;}

 void opCall()
 {
 if(isDelegate)
 dg();
 else
 fn();
 }
 }


 Waow, very nice solution.
 I really question the function/delegate distinction (mostly artificial,  
 imo) that "invents" issues necessiting workarounds like that. What does  
 it mean, what does it bring?


A function pointer is compatible with a C function pointer.  C does not  
have delegates, so if you want to do callbacks, you need to use function  
pointers.  There is no way to combine them and keep C compatibility.


 Right, there is one pointer less for funcs. This save 4 or 8 bytes, so  
 to say, nothing; who develops apps with arrays of billions of funcs?  
 There are written in source ;-) Even then, if this saving of apointer  
 was of any relevance, then it should be an implementation detail that  
 does not leak into artificial semantic diff, creating issues on the  
 programmer side. What do you think?


What you want is already implemented.  There is a relatively new phobos  
construct that builds a delegate out of a function pointer.  In fact, my  
code could use it and save the tag:


// again, untested!

import std.functional : toDelegate;

struct Example
{
    private void delegate() dg;

    void setCallback(void function() f) { this.dg = toDelegate(f); }
    void setCallback(void delegate() d) { this.dg = d; }

    void opCall() { dg(); }
}

Note that toDelegate doesn't appear on the docs because of a doc  
generation bug...

-Steve
Feb 10 2011
next sibling parent reply useo <useo start.bg> writes:
I implemented all I wanted and it works perfectly ;).

But I'm using the "if (is(T == delegate) || is(T == function))"-
statement in another class/template.

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

Now, when I declare Example!(void function()) myVar; I always get:

Error: template instance Example!(void function()) does not match
template declaration Example(T) if (is(T == delegate) || is(T ==
function))
Error: Example!(void function()) is used as a type

When I declare myVar as Example!(function), I get some other errors.

What's wrong with my code?
Feb 10 2011
parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Thu, 10 Feb 2011 09:09:03 -0500, useo <useo start.bg> wrote:


 I implemented all I wanted and it works perfectly ;).

 But I'm using the "if (is(T == delegate) || is(T == function))"-
 statement in another class/template.

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

 Now, when I declare Example!(void function()) myVar; I always get:

 Error: template instance Example!(void function()) does not match
 template declaration Example(T) if (is(T == delegate) || is(T ==
 function))
 Error: Example!(void function()) is used as a type

 When I declare myVar as Example!(function), I get some other errors.

 What's wrong with my code?


Please post a full example that creates the error.  From that error  
message, it appears that your code is correct, but I'd have to play with a  
real example to be sure.

-Steve
Feb 10 2011
parent reply useo <useo start.bg> writes:
== Auszug aus Steven Schveighoffer (schveiguy yahoo.com)'s Artikel

 On Thu, 10 Feb 2011 09:09:03 -0500, useo <useo start.bg> wrote:

 I implemented all I wanted and it works perfectly ;).

 But I'm using the "if (is(T == delegate) || is(T == function))"-
 statement in another class/template.

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

 Now, when I declare Example!(void function()) myVar; I always get:

 Error: template instance Example!(void function()) does not match
 template declaration Example(T) if (is(T == delegate) || is(T ==
 function))
 Error: Example!(void function()) is used as a type

 When I declare myVar as Example!(function), I get some other




errors.

 What's wrong with my code?


 Please post a full example that creates the error.  From that error
 message, it appears that your code is correct, but I'd have to play


with a

 real example to be sure.
 -Steve


I created a complete, new file with the following code:

module example;

void main(string[] args) {
	Example!(void function()) myVar;
}

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

And what I get is:

example.d(4): Error: template instance Example!(void function()) does
not match template declaration Example(T) if (is(T == delegate) || is
(T == function))
example.d(4): Error: Example!(void function()) is used as a type

I'm using the current stable version 2.051.
Feb 10 2011
next sibling parent useo <useo start.bg> writes:
== Auszug aus useo (useo start.bg)'s Artikel

 == Auszug aus Steven Schveighoffer (schveiguy yahoo.com)'s Artikel

 On Thu, 10 Feb 2011 09:09:03 -0500, useo <useo start.bg> wrote:

 I implemented all I wanted and it works perfectly ;).

 But I'm using the "if (is(T == delegate) || is(T == function))"-
 statement in another class/template.

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

 Now, when I declare Example!(void function()) myVar; I always






get:

 Error: template instance Example!(void function()) does not






match

 template declaration Example(T) if (is(T == delegate) || is(T ==
 function))
 Error: Example!(void function()) is used as a type

 When I declare myVar as Example!(function), I get some other




 errors.

 What's wrong with my code?


 Please post a full example that creates the error.  From that




error

 message, it appears that your code is correct, but I'd have to




play

 with a

 real example to be sure.
 -Steve


 I created a complete, new file with the following code:
 module example;
 void main(string[] args) {
 	Example!(void function()) myVar;
 }
 class Example(T) if (is(T == delegate) || is(T == function)) {
 }
 And what I get is:
 example.d(4): Error: template instance Example!(void function())


does

 not match template declaration Example(T) if (is(T == delegate) ||


is

 (T == function))
 example.d(4): Error: Example!(void function()) is used as a type
 I'm using the current stable version 2.051.


I noticed, that this error only occurs when I use function as
template-type. When I use Example!(void delegate()) myVar; it
compiles without any error. With function - Example!(void function())
myVar; I get the error(s) above.
Feb 10 2011
prev sibling parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Thu, 10 Feb 2011 09:48:14 -0500, useo <useo start.bg> wrote:



 I created a complete, new file with the following code:

 module example;

 void main(string[] args) {
 	Example!(void function()) myVar;
 }

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

 And what I get is:

 example.d(4): Error: template instance Example!(void function()) does
 not match template declaration Example(T) if (is(T == delegate) || is
 (T == function))
 example.d(4): Error: Example!(void function()) is used as a type

 I'm using the current stable version 2.051.


Found this invalid bug.  Apparently, this is expected (!) behavior:

http://d.puremagic.com/issues/show_bug.cgi?id=3464

So use this instead:

class Example(T) if (is(T == delegate) || is(typeof(*T.init) == function))

Ugly, I know, but I guess that's what we got to work with.

-Steve
Feb 10 2011
parent useo <useo start.bg> writes:
== Auszug aus Steven Schveighoffer (schveiguy yahoo.com)'s Artikel

 On Thu, 10 Feb 2011 09:48:14 -0500, useo <useo start.bg> wrote:

 I created a complete, new file with the following code:

 module example;

 void main(string[] args) {
 	Example!(void function()) myVar;
 }

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

 And what I get is:

 example.d(4): Error: template instance Example!(void function())




does

 not match template declaration Example(T) if (is(T == delegate)




|| is

 (T == function))
 example.d(4): Error: Example!(void function()) is used as a type

 I'm using the current stable version 2.051.


 Found this invalid bug.  Apparently, this is expected (!) behavior:
 http://d.puremagic.com/issues/show_bug.cgi?id=3464
 So use this instead:
 class Example(T) if (is(T == delegate) || is(typeof(*T.init) ==


function))

 Ugly, I know, but I guess that's what we got to work with.
 -Steve


Yes, looks a bit unusual but it works, thanks!
Feb 10 2011
prev sibling parent reply spir <denis.spir gmail.com> writes:
On 02/10/2011 02:51 PM, Steven Schveighoffer wrote:

 On Thu, 10 Feb 2011 08:39:13 -0500, spir <denis.spir gmail.com> wrote:


 On 02/09/2011 11:05 PM, Steven Schveighoffer wrote:



 I don't think you want templates. What you want is a tagged union (and a struct
 is MUCH better suited for this):

 // untested!

 struct Example
 {
 private
 {
 bool isDelegate;
 union
 {
 void function() fn;
 void delegate() dg;
 }
 }

 void setCallback(void function() f) { this.fn = f; isDelegate = false;}
 void setCallback(void delegate() d) { this.dg = d; isDelegate = true;}

 void opCall()
 {
 if(isDelegate)
 dg();
 else
 fn();
 }
 }


 Waow, very nice solution.
 I really question the function/delegate distinction (mostly artificial, imo)
 that "invents" issues necessiting workarounds like that. What does it mean,
 what does it bring?


 A function pointer is compatible with a C function pointer. C does not have
 delegates, so if you want to do callbacks, you need to use function pointers.
 There is no way to combine them and keep C compatibility.


 Right, there is one pointer less for funcs. This save 4 or 8 bytes, so to
 say, nothing; who develops apps with arrays of billions of funcs? There are
 written in source ;-) Even then, if this saving of apointer was of any
 relevance, then it should be an implementation detail that does not leak into
 artificial semantic diff, creating issues on the programmer side. What do you
 think?


 What you want is already implemented. There is a relatively new phobos
 construct that builds a delegate out of a function pointer. In fact, my code
 could use it and save the tag:


 // again, untested!

 import std.functional : toDelegate;

 struct Example
 {
 private void delegate() dg;

 void setCallback(void function() f) { this.dg = toDelegate(f); }
 void setCallback(void delegate() d) { this.dg = d; }

 void opCall() { dg(); }
 }

 Note that toDelegate doesn't appear on the docs because of a doc generation
bug...


Right.

I had not thought at the C-compatibility issue. So, let us say the func/dg 
distinction must remain in the language, on programmer-side, because of that. 
Then, is there anything that prevent the above cast to be implicit? Then, 
programmers would only have to define a single interface, using delegate 
everywhere; and not care about where and how user funcs are defined.
(because as you know presently whether a ref'ed func becomes a func pointer or 
a delegate depends on /where/ it is defined...)

Second point. I would like referencing of functions/delegates passed as 
arguments to be implicite. After all, conceptually, what we pass is a "function 
object". Not a pointer. That the implementation needs to "point" them is just 
this, implementation. The '&' just pollutes the code meaninglessly; and it's 
absence creates weird bugs:

void f0 (     ) { writeln(1); }
void f1 (int i) { writeln(i); }
void do0 (void function (   ) f) { f( ); }
void do1 (void function (int) f) { f(3); }

unittest {
     // Error: function __trials__.do0 (void function() f) is not callable
     // using argument types (void)
     do0(f0);

     // __trials__.d(46): Error: function __trials__.f1 (int i) is not callable
     // using argument types ()
     do1(f1);

     do0(&f0);   // ok
     do1(&f1);   // ok
}

Error messages are difficult to interpret for a diagnosis, I guess. Note that 
the first one concerns the caller, while the second one concerns the callee...
Implicite referencing would solve that issue /and/ match semantics /and/ be 
more consistent /and/ make code nicer. About consistency, I mean that functions 
are already implicitely dereferenced: do1 does not need to call its arg f using
	(*f)(3);
(this version works as well, indeed)

denis
-- 
_________________
vita es estrany
spir.wikidot.com
Feb 10 2011
parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Thu, 10 Feb 2011 12:04:28 -0500, spir <denis.spir gmail.com> wrote:


 On 02/10/2011 02:51 PM, Steven Schveighoffer wrote:

 On Thu, 10 Feb 2011 08:39:13 -0500, spir <denis.spir gmail.com> wrote:


 On 02/09/2011 11:05 PM, Steven Schveighoffer wrote:



 I don't think you want templates. What you want is a tagged union  
 (and a struct
 is MUCH better suited for this):

 // untested!

 struct Example
 {
 private
 {
 bool isDelegate;
 union
 {
 void function() fn;
 void delegate() dg;
 }
 }

 void setCallback(void function() f) { this.fn = f; isDelegate =  
 false;}
 void setCallback(void delegate() d) { this.dg = d; isDelegate = true;}

 void opCall()
 {
 if(isDelegate)
 dg();
 else
 fn();
 }
 }


 Waow, very nice solution.
 I really question the function/delegate distinction (mostly  
 artificial, imo)
 that "invents" issues necessiting workarounds like that. What does it  
 mean,
 what does it bring?


 A function pointer is compatible with a C function pointer. C does not  
 have
 delegates, so if you want to do callbacks, you need to use function  
 pointers.
 There is no way to combine them and keep C compatibility.


 Right, there is one pointer less for funcs. This save 4 or 8 bytes, so  
 to
 say, nothing; who develops apps with arrays of billions of funcs?  
 There are
 written in source ;-) Even then, if this saving of apointer was of any
 relevance, then it should be an implementation detail that does not  
 leak into
 artificial semantic diff, creating issues on the programmer side. What  
 do you
 think?


 What you want is already implemented. There is a relatively new phobos
 construct that builds a delegate out of a function pointer. In fact, my  
 code
 could use it and save the tag:


 // again, untested!

 import std.functional : toDelegate;

 struct Example
 {
 private void delegate() dg;

 void setCallback(void function() f) { this.dg = toDelegate(f); }
 void setCallback(void delegate() d) { this.dg = d; }

 void opCall() { dg(); }
 }

 Note that toDelegate doesn't appear on the docs because of a doc  
 generation bug...


 Right.

 I had not thought at the C-compatibility issue. So, let us say the  
 func/dg distinction must remain in the language, on programmer-side,  
 because of that. Then, is there anything that prevent the above cast to  
 be implicit? Then, programmers would only have to define a single  
 interface, using delegate everywhere; and not care about where and how  
 user funcs are defined.
 (because as you know presently whether a ref'ed func becomes a func  
 pointer or a delegate depends on /where/ it is defined...)

 Second point. I would like referencing of functions/delegates passed as  
 arguments to be implicite. After all, conceptually, what we pass is a  
 "function object". Not a pointer. That the implementation needs to  
 "point" them is just this, implementation. The '&' just pollutes the  
 code meaninglessly;


This is the way it is in C, and D purposely does not do this to avoid  
ambiguity (did you want to call the function or get it's address?).


 and it's absence creates weird bugs:

 void f0 (     ) { writeln(1); }
 void f1 (int i) { writeln(i); }
 void do0 (void function (   ) f) { f( ); }
 void do1 (void function (int) f) { f(3); }

 unittest {
      // Error: function __trials__.do0 (void function() f) is not  
 callable
      // using argument types (void)
      do0(f0);

      // __trials__.d(46): Error: function __trials__.f1 (int i) is not  
 callable
      // using argument types ()
      do1(f1);

      do0(&f0);   // ok
      do1(&f1);   // ok
 }

 Error messages are difficult to interpret for a diagnosis, I guess. Note  
 that the first one concerns the caller, while the second one concerns  
 the callee...
 Implicite referencing would solve that issue /and/ match semantics /and/  
 be more consistent /and/ make code nicer. About consistency, I mean that  
 functions are already implicitely dereferenced: do1 does not need to  
 call its arg f using
 	(*f)(3);
 (this version works as well, indeed)


When properties are properly implemented, I expect this error message to  
be different.  Currently, it thinks you are trying to call the function f0  
and pass its result to do0.

-Steve
Feb 10 2011
prev sibling parent bearophile <bearophileHUGS lycos.com> writes:
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
Feb 09 2011