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Subject: Re: Why is std::array an aggregate?
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James Kanze wrote:

> On Dec 18, 9:00 pm, Scott Meyers <NeverR...@aristeia.com> wrote:
>> In TR1, std::tr1::array needed to be an aggregate so that it
>> could be brace-initialized.  To offer the same capability for
>> C++0x's std::array, the class could simply declare a
>> constructor taking a std::initializer_list.  So why is
>> std::array an aggregate?  Making it a non-aggregate would
>> permit e.g., giving it a constructor taking a pair of
>> iterators.
> 
> Presumably, so that it can be statically initialized, in order
> to avoid order of initialization problems.  
>

I believe this can all be done using variadic templates:

template<typename T, size_t S>
struct array {
   template<typename ...U>
   constexpr array(U&&... u):elems{ u... } { }

   T elems[S];
};

array<int, 3> a = { 1, 2 }; // works, is statically initialized
array<int, 2> a = { 1, 2, 3 }; // gives an error at compile time

It doesn't seem to be that we can use static_cast or std::forward here to
enable move semantics, as i think it will render the initializers to non-
potential-constant-expressions.

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