An attempt to create a member of a struct with constexpr attribute without being static result in a compiler error(see below). Why is that? for a single constant value will I have this value in memory until program is terminatted instead of just scope of struct? should I back to use a macro?
struct foo
{
constexpr int n = 10;
// ...
};
error: non-static data member cannot be constexpr; did you intend to make it static?
I don't know the official rational. But surely it could lead to confusion. I, for one, can't see what it means for a non-static data member to be constexpr. Are you able to do the following?
struct foo {
constexpr int n = 10;
constexpr foo() { }
constexpr foo(int n):n(n) { } // overwrite value of n
};
Or does it mean that the initializer must be constant always, i.e you are not allowed to write the above (because n is not constant/could potentially non-constant) but allowed to say
foo f = { 10 };
The rule that constexpr int n is simply ill-formed rather than being implicitly static seems good to me, as its semantics would not be clear IMO.
constexpr int n = 10 as it is an integral type every use of n during compilation should be substituted with its value just like in case of define. The syntax is pretty clear, I don't understand why the standard doesn't allow it.
constexprfor each object?constexpris compile-time only, right? So if that's the case, why would you have one per instance? It wouldn't exist at runtime.