Signature conditions

[Timon Gehr]

On 02/10/2012 07:50 PM, H. S. Teoh wrote:
> On Fri, Feb 10, 2012 at 07:36:38PM +0100, David Nadlinger wrote:
>> On 2/10/12 7:35 PM, David Nadlinger wrote:
>>> class(T) if (__traits(compiles, { std.utf.decode(T.init); } )) { … }
>>
>> (untested, you might have to return the value from the delegate to
>> avoid an expression-without-effect error)
>
> Works for me. Thanks!!
>
> On that note, I discovered that if you want signature constraints on a
> derived class, the syntax is unbearably ugly:
>
> 	class Derived(T)
> 		if (/* conditions */)
> 		: Base
> 	{
> 		...
> 	}
>
> I would have expected the syntax to be like this instead:
>
> 	class Derived(T) : Base
> 		if (/* conditions */)
> 	{
> 		...
> 	}
>
> But this doesn't compile.
>
>
> T
>

It makes more sense as it is. Consider the instantiation 'Derived!int' 
and the condition 'is(typeof(T)==class)'.