Say I have a class that that can return a constant expression through a constexpr
function:
template
struct Foo {
constexpr int Bar()
§5.20:
The reference does not have a preceding initialization from the point of view of i
, though: It's a parameter. It's initialized once ByReference
is called.
Let's remove the constexpr
from i
's declaration and consider an invocation of ByReference
in its entirety:
template
constexpr int ByReference(const Foo &f) {
int i = f.Bar();
return i;
}
constexpr int j = ByReference(Foo<0>());
This is fine, since f
does have preceding initialization. The initializer of f
is a constant expression as well, since the implicitly declared default constructor is constexpr
in this case (§12.1/5).
Hence i
is initialized by a constant expression and the invocation is a constant expression itself.