constexpr errors; VS2017 C++ compiler regression?

问题

Just installed VS2017, which claims to have superior C++14 support since 2015 (which was rudimentary). Gave it a spin on one of my projects which uses constexpr, and noticed what appear to be some regressions.

This code:

struct s
{
    size_t i;
    constexpr s(nullptr_t) noexcept : i(0) {}
};
static_assert(s(nullptr).i == 0, "!!");

Compiles no problem on VS2015 and Clang, but I get a new error in VS2017:

error C2131: expression did not evaluate to a constant
note: failure was caused by unevaluable pointer value
note: while evaluating 's::s(&s{(null)})'

This code looks fine right? Is constexpr meant to have a problem with nullptr?
I'm astonished a regression this basic could appear, I suspect there must be something wrong with my code...

回答1:

constexpr constructor(std::nullptr_t) causes "error C2131: expression did not evaluate to a constant"

This issue was reported as a bug in Visual Studio 2017 version 15.1.
There was a variation of another issue reported earlier by the OP (?).

This was fixed in: Visual Studio 2017 version 15.6 Preview 1

来源：https://stackoverflow.com/questions/42917099/constexpr-errors-vs2017-c-compiler-regression