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std::piecewise_construct , defined in <utility>, has internal linkage since it is declared constexpr . I wonder if use of std::piecewise_construct in a header can violate ODR. For example: a.hpp #include <utility> #include <tuple> struct point { point(int x, int y) : x(x), y(y) {} int x, y; }; inline std::pair<point, point> f(int x1, int y1, int x2, int y2) { return { std::piecewise_construct, std::forward_as_tuple(x1, y1), std::forward_as_tuple(x2, y2) }; } translation unit 1 #include "a.hpp" translation unit 2 #include "a.hpp" The std::piecewise_construct in f in TU 1 refers to a different object than that in f in TU 2. I suspect f violates ODR. N3290 (probably ISO/IEC 14882:2011 also) says the following case is an exception of ODR, in 3.2/5: a name can refer to a const object with internal or no linkage if the object has the same literal type in all definitions of D, and the object is initialized with a constant expression (5.19), and the value (but not the address) of the object is used, and the object has the same value in all definitions of D; f satisfies almost all the requirements, but "the value (but not the address) of the object is used" seems ambiguous to me. It's true that std::piecewise_construct_t has no state, but a call of the piecewise constructor of std::pair involves a call of the implicit-declared copy constructor of std::piecewise_construct_t , whose argument is const std::piecewise_construct_t & . The address is "used", isn't it? I'm very puzzled. Reference: <a href="http://lists.boost.org/Archives/boost/2007/06/123353.php" rel="nofollow

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