This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115d. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2024-10-26
[Adopted at the February, 2016 meeting.]
Consider the following example:
template<int> struct X { typedef int type; }; template<typename T> struct Y { void f() { X<false ? this - this : 0>::type x; } // missing typename? }; void g() { Y<void>().f(); }
This appears to be valid because the template argument expression is not value-dependent.
Until I discovered this, I had been assuming that any type-dependent expression is also value-dependent. The only exception to that appears to be the expression this, which may be type-dependent but is never value-dependent.
Now, this need not ever be value-dependent, because evaluation of it will never succeed when it appears as a subexpression of an expression that we're checking for constant-expression-ness. But if that's really what we want here, then the same applies to function parameters with dependent types, and probably a few other cases.
Proposed resolution (September, 2015) [SUPERSEDED]:
Change 13.8.3.4 [temp.dep.constexpr] paragraph 4 as follows:
Expressions of the following form are value-dependent:
sizeof ... ( identifuer )
this
fold-expression
Proposed resolution (March, 2016):
This issue is resolved by the resolution of issue 2109.