[Bug libstdc++/53248] std::array<T,0> doesn't work when T is not default-constructible

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53248

Daniel Krügler <daniel.kruegler at googlemail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |daniel.kruegler at
                   |                            |googlemail dot com

--- Comment #1 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2012-05-05 21:16:36 UTC ---
(In reply to comment #0)
> Looking at <array> on the web at your documentation pages, there is no
> specialization of "std::array<T,N>" for "std::array<T,0>"; you just nudge the
> element count to 1 when it would have been zero.  That secret element still
> needs to be specified, since std::type_index doesn't have a default
> constructor, although no initializers are logically necessary for an empty
> array (i.e. the work-around abstraction leaks).
> 
> The first way I see around it is to make an explicit specialization that's
> data-less.

While I completely agree with your suggestion but I need to say that
unfortunately this is not what the library specification requires. The current
wording in fact allows implementations of the form found here. There is (again:
unfortunately) nothing that requires that std::array<T, 0> shall be
default-constructible irrespective of whether T is default-constructible, for
example.

I cannot speak for the decisions made in libstdc++ in regard to std::array's
optimized zero-size support, but I would like to encourage you to submit a
library issue to the email-address in the beginning of

http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html

for this matter. I really think that it should be required that std::array<T,
0> is always default-constructible.