[phobos] isClass!T

[Lars Tandle Kyllingstad]

I ran into it with std.traits.hasMember!(T, "foo"), which always
evaluates to false if T is an interface.
https://github.com/D-Programming-Language/phobos/blob/master/std/traits.d#L1537

Other examples include:

std.conv.emplace(),
https://github.com/D-Programming-Language/phobos/blob/master/std/conv.d#L4044
https://github.com/D-Programming-Language/phobos/blob/master/std/conv.d#L4064
https://github.com/D-Programming-Language/phobos/blob/master/std/conv.d#L4158

std.traits.StringTypeOf,
https://github.com/D-Programming-Language/phobos/blob/master/std/traits.d#L3181

std.typecons.tuple.toString (I think),
https://github.com/D-Programming-Language/phobos/blob/master/std/typecons.d#L508

std.typecons.RefCounted,
https://github.com/D-Programming-Language/phobos/blob/master/std/typecons.d#L2272

std.variant.VariantN.opAssign (I think),
https://github.com/D-Programming-Language/phobos/blob/master/std/variant.d#L520

-Lars



On Thu, 2011-05-19 at 08:17 -0700, Steve Schveighoffer wrote:
> Can you give some examples of where it should be fixed?
> 
> 
> -Steve
> 
> 
>         
>         ______________________________________________________________
>         From: Lars Tandle Kyllingstad <lars at kyllingen.net>
>         To: Phobos mailing list <phobos at puremagic.com>
>         Sent: Thursday, May 19, 2011 11:11 AM
>         Subject: [phobos] isClass!T
>         
>         Several places in Phobos I've noticed tests like
>         if(is(T==class)) that
>         check whether T is a class type.  I suspect it is usually
>         meant for
>         these tests to pass if T is an interface as well, but this is
>         not the
>         case.  Doing
>         
>           grep 'is(\w\+\s*==\s*class)' *.d
>         
>         on the Phobos sources reveals many cases where the test for
>         is(T==interface) has most likely been forgotten.  This should
>         be fixed,
>         and I think the best way is to add the following to
>         std.traits:
>         
>           template isClass(T)
>           {
>               enum isClass = is(T == class) || is(T == interface);
>           }
>         
>         Most instances of is(T==class) in Phobos can then be replaced
>         with
>         isClass!T.
>         
>         What say you?
>         
>         -Lars
>         
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