This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 117a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2025-04-13
1911. constexpr constructor with non-literal base classSection: 9.2.6 [dcl.constexpr] Status: CD4 Submitter: Richard Smith Date: 2014-04-13[Moved to DR at the November, 2014 meeting.]
An example like
struct X {
std::unique_ptr<int> p;
constexpr X() { }
};
is ill-formed because the X constructor cannot be used in a constant expression, because a constant expression cannot construct an object of a non-literal type like unique_ptr. This prevents use of something like
X x;
to guarantee constant-initialization.
Proposed resolution (June, 2014):
Change 9.2.6 [dcl.constexpr] paragraph 5 as follows:
For a non-template, non-defaulted constexpr function or a non-template, non-defaulted, non-inheriting constexpr constructor, if no argument values exist such that an invocation of the function or constructor could be an evaluated subexpression of a core constant expression (7.7 [expr.const]), or, for a constructor, a constant initializer for some object (6.9.3.2 [basic.start.static]), the program is ill-formed; no diagnostic required.
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