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We ran into this with an std::function (libstdc++ 13) returning an object with protected copy constructor. It boils down to this:
class X {
protected:
X(const X&);
};
static_assert(!__reference_converts_from_temporary(X, X));
template<typename A, typename B,
bool Dangle = __reference_converts_from_temporary(A, B)>
static void test();
using Result = decltype(test<X, X>());produces:
bug.cpp:9:24: error: calling a protected constructor of class 'X'
9 | bool Dangle = __reference_converts_from_temporary(A, B)>
| ^
Replacing either A or B by X doesn't make the error go away. Interestingly, if we define test, for example with an empty body, and do a full instantiation, then the error appears if the instantiation is implicit, but not if it's explicit:
template<typename A, typename B,
bool Dangle = __reference_converts_from_temporary(A, B)>
static void test() {} // <-- Added an empty body.
template void test<X, X>(); // No error.
void f() {
test<X, X>(); // Error.
}Metadata
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Language frontend issues, e.g. anything involving "Sema"Language frontend issues, e.g. anything involving "Sema"