I'm not quite sure how to do this, but I'm sure one of you does. I need something like:

static if ( functionExists(char[] .toString(T)) ) { ... }

static if ( functionExists(char[] T.toString()) ) { ... }

What is the real way to do this static check?

Thanks!

-- 
Michiel

Look in d.D.learn, there's a recent topic named
 -> "Testing if a function is defined in a module"
I guess that will help you.

David

Michiel schrieb:
> I'm not quite sure how to do this, but I'm sure one of you does. I need
> something like:
> 
> static if ( functionExists(char[] .toString(T)) ) { ... }
> 
> static if ( functionExists(char[] T.toString()) ) { ... }
> 
> What is the real way to do this static check?
> 
> Thanks!
> 

On Wed, 21 Feb 2007 21:25:20 +0100, Michiel <nomail@please.com> wrote:

>I'm not quite sure how to do this, but I'm sure one of you does. I need something like:
>
>static if ( functionExists(char[] .toString(T)) ) { ... }
>
>static if ( functionExists(char[] T.toString()) ) { ... }
>
>What is the real way to do this static check?
>
>Thanks!

The way that I can think of is

static if (is(typeof(&T.toString) == char[] function()))

There might be others

Michiel wrote:
> I'm not quite sure how to do this, but I'm sure one of you does. I need
> something like:
> 
> static if ( functionExists(char[] .toString(T)) ) { ... }
> 
> static if ( functionExists(char[] T.toString()) ) { ... }
> 
> What is the real way to do this static check?
> 
> Thanks!
> 
Check out this (http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D.learn&article_id=6577) thread in digitalmars.D.learn.  It answers your question exactly.  For non-static member functions of classes you'll need to test against a reference to that class (although it doesn't need to be initialized).  To get the return and parameter types you can use the templates in std.traits (note: those templates (and DMD itself) will only reveal the first overload of a function; there is no way to get the parameter list for others).

Tyler Knott wrote:

>> I'm not quite sure how to do this, but I'm sure one of you does. I need something like:
>>
>> static if ( functionExists(char[] .toString(T)) ) { ... }
>>
>> static if ( functionExists(char[] T.toString()) ) { ... }
>>
>> What is the real way to do this static check?
>>
>> Thanks!
>>
> Check out this (http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D.learn&article_id=6577) thread in digitalmars.D.learn.  It answers your question exactly.

Well, not exactly. They only check for the function name, while I also need to check out the parameter.

And if I really want to do it right, also the return type. But I suppose a function named toString will probably return char[], so that's less important.

> For
> non-static member functions of classes you'll need to test against a
> reference to that class (although it doesn't need to be initialized).
> To get the return and parameter types you can use the templates in
> std.traits (note: those templates (and DMD itself) will only reveal the
> first overload of a function; there is no way to get the parameter list
> for others).

That's too bad. Because std.string.toString is exactly the function I want to check for (among other, self-defined toString functions). And there are 20 such functions, all with a different parameter type.

I don't really need the whole list of parameters anyway. I only want to know if a function with a parameter type I specify exists or not.

-- 
Michiel

Max Samukha wrote:

>> static if ( functionExists(char[] T.toString()) ) { ... }
> 
> The way that I can think of is
> 
> static if (is(typeof(&T.toString) == char[] function()))

Thanks! That part works great. The only thing missing now is the
toString(T) part.

-- 
Michiel

david wrote:

> Look in d.D.learn, there's a recent topic named
>  -> "Testing if a function is defined in a module"
> I guess that will help you.

See other reply.

Thanks!

-- 
Michiel

Michiel wrote:
> Tyler Knott wrote:
> 
>>> I'm not quite sure how to do this, but I'm sure one of you does. I need
>>> something like:
>>>
>>> static if ( functionExists(char[] .toString(T)) ) { ... }
>>>
>>> static if ( functionExists(char[] T.toString()) ) { ... }
>>>
>>> What is the real way to do this static check?
>>>
>>> Thanks!
>>>
>> Check out this
>> (http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D.learn&article_id=6577)
>> thread in digitalmars.D.learn.  It answers your question exactly.
> 
> Well, not exactly. They only check for the function name, while I also
> need to check out the parameter.
> 
> And if I really want to do it right, also the return type. But I suppose
> a function named toString will probably return char[], so that's less
> important.
> 
>> For
>> non-static member functions of classes you'll need to test against a
>> reference to that class (although it doesn't need to be initialized). To get the return and parameter types you can use the templates in
>> std.traits (note: those templates (and DMD itself) will only reveal the
>> first overload of a function; there is no way to get the parameter list
>> for others).
> 
> That's too bad. Because std.string.toString is exactly the function I
> want to check for (among other, self-defined toString functions). And
> there are 20 such functions, all with a different parameter type.
> 
> I don't really need the whole list of parameters anyway. I only want to
> know if a function with a parameter type I specify exists or not.
> 
Hmm... I've only ever tried to get backwards (from knowing the function name to knowing all the overloads).  It seems that it's possible to find out if there's an overload for a specific parameter list:

import std.string;

class x{}
class y{}
extern char[] toString(x y);
void main()
{
	static if(is(typeof(toString(cast(x)null)))) pragma(msg, "This works.");

	//Note: you need to use the fully qualified name of toString if there's another toString in the local scope,
	//even if it uses a different overload which fits the type better.
	static if(is(typeof(std.string.toString(cast(uint)5)))) pragma(msg, "This too.");

	static if(is(typeof(toString(cast(y)null)))) pragma(msg, "Not this.");
}

For all types you can use T.init as the dummy value to the function (I just remembered its existence).

On Wed, 21 Feb 2007 15:32:52 -0600, Tyler Knott <tywebmail@mailcity.com> wrote:

>For all types you can use T.init as the dummy value to the function (I just remembered its existence).

This works for module scope functions:

static if (is(typeof(&.toString) == char[] function(T))) // '.' is the
module scope operator or use fully qualified name. Trickier ways might
exist.