How is the correct way of mix  Pre and Post contracts and signature constraints ?

I try this that looks logic way and not compile :

T foo (T) (T a)
if ( is(T : real)) {
 in {
	assert (a > 0);
 }
 body {
	return a*2;
 }
}

I get this errors :
Declaration expected, not 'if'
unrecognized declaration

And this with same result :

T foo (T) (T a)
in {
	assert (a > 0);
}
if ( is(T : real)) {
 body {
	return a*2;
 }
}

I'm using dmd 2.053.

-- 
Yep, I'm afraid that I have a blog : zardoz.es

On 04.07.2011 19:20, Zardoz wrote:
> How is the correct way of mix  Pre and Post contracts and signature constraints ?
>
> I try this that looks logic way and not compile :
>
> T foo (T) (T a)
> if ( is(T : real)) {
>   in {
> 	assert (a>  0);
>   }
>   body {
> 	return a*2;
>   }
> }
>
> I get this errors :
> Declaration expected, not 'if'
> unrecognized declaration
>
> And this with same result :
>
> T foo (T) (T a)
> in {
> 	assert (a>  0);
> }
> if ( is(T : real)) {
>   body {
> 	return a*2;
>   }
> }
>
> I'm using dmd 2.053.
>

The "in" should be in a block of it's own:

T foo(T)(T a)
if(...) // notice no { here
in {
} body {
}

On 04.07.2011 19:42, simendsjo wrote:
>
> The "in" should be in a block of it's own:
>
> T foo(T)(T a)
> if(...) // notice no { here
> in {
> } body {
> }

I of course mean that if should not create a new block.

On Mon, 04 Jul 2011 19:52:10 +0200, simendsjo wrote:

> On 04.07.2011 19:42, simendsjo wrote:
>>
>> The "in" should be in a block of it's own:
>>
>> T foo(T)(T a)
>> if(...) // notice no { here
>> in {
>> } body {
>> }
> 
> I of course mean that if should not create a new block.
Thanks !
I thought that the if () needs to make a block. :P




-- 
Yep, I'm afraid that I have a blog : zardoz.es

On 04.07.2011 20:12, Zardoz wrote:
> On Mon, 04 Jul 2011 19:52:10 +0200, simendsjo wrote:
>
>> On 04.07.2011 19:42, simendsjo wrote:
>>>
>>> The "in" should be in a block of it's own:
>>>
>>> T foo(T)(T a)
>>> if(...) // notice no { here
>>> in {
>>> } body {
>>> }
>>
>> I of course mean that if should not create a new block.
> Thanks !
> I thought that the if () needs to make a block. :P

The if is called a template constrain: http://www.d-programming-language.org/template.html#Constraint

T foo(T)(T a) is a shorthand (I think) for

template foo(T) {
  T foo(T a) {
  }
}

The constraint refers to the template part:

template foo(T) if(is(T:real)) {
  T foo(T a) {
  }
}

Because the template only contain a single member, and it's named the same as the template, you can instantiate it directly as foo(1.2);
If the function was named bar, you'd have to instantiate it yourself: foo!real.bar(1.2);