Is it legal to declare a constexpr initializer_list object?

Question

As a question that came up during the discussion of this SO question:

Is it legal, maybe with N3471, to declare a constexpr std::initializer_list object

Answer 1

Update: The situation got a bit more complicated after the resolution of CWG DR 1684 removed the requirement quoted below. Some more information can be found in this discussion on the std-discussion mailing list and in the related question Why isn't `std::initializer_list` defined as a literal type?

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[decl.constexpr]/8:

A constexpr specifier for a non-static member function that is not a constructor declares that member function to be const (9.3.1). [...] The class of which that function is a member shall be a literal type (3.9).

Therefore, the changes of N3471 guarantee std::initializer_list will be a literal type.

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Note the constexpr ctor alone doesn't require std::initializer_list to be a literal type, see [dcl.constexpr]/4+8. Side note: An object of non-literal type with constexpr ctor can be initialized during constant initialization [basic.start.init]/2] (part of static initialization, performed before any dynamic initialization).