struct A { int i; };

根据规范[expr.ref](我用n4618)：

(if E2 is non-reference,) …If E1 is an lvalue,then E1.E2 is an lvalue; otherwise E1.E2 is an xvalue…

显然A {}.我是x值;
也给了[dcl.type.simple]：

(for decltype(e),) — … if e is an unparenthesized id-expression or an unparenthesized class member access…
— otherwise,if e is an xvalue,decltype(e) is T&&,where T is the type of e

因此,decltype((A {}.i))将产生int&&

然而,我尝试过GCC5.1和Clang3.9,它们产生int,而vs2015u3产生int&&哪个是对的？