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Date: Sun, 07 Jun 2015 08:49:00 -0000
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Subject: Re: [v3 PATCH] Implement N4387 and LWG 2367
From: Ville Voutilainen <ville.voutilainen@gmail.com>
To: libstdc++@gcc.gnu.org
Cc: "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
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On 7 June 2015 at 11:12, Ville Voutilainen <ville.voutilainen@gmail.com> wrote:
>> Does the following code still compile with your patch?
>> struct A { int a,b; };
>> std::tuple<int,int,A> a(3,4,{1,2});
>
> No. :/ And we have no test for it.. I'll need to look at that.

Ahem, yes, this is because the constructor that used to take _Elements
now takes _UElements. I can change it back to take _Elements, because
the technique that the default constructors use allow making the signature
dependent enough that it will sfinae correctly.

>> You use a lot: typename enable_if<X, bool>::type=true
>> while the current code seems to favor: class=typename enable_if<X>::type.
>> I don't really care which one is used, but it is easier to read when the
>> style is consistent through the library.
> It's not a style issue. That template parameter needs to be a non-type one,
> otherwise the overloads are ambiguous.

...and I think it doesn't necessarily need to be non-type, I think it can be
made to work with a type parameter that is enable_if<X, true_type>
and enable_if<X, false_type> for the mutually-exclusive overloads.