https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95066
--- Comment #1 from Owen Smith <ojman101 at protonmail dot com> ---
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#include <type_traits>
template <typename, typename>
class IsSafelyCastable : public std::false_type {};
template <>
class IsSafelyCastable<int, float> : public std::true_type {};
template <typename T>
struct Foo {
template <typename U>
explicit(!IsSafelyCastable<T, U>::value) operator Foo<U>() { return {}; }
};
int main() {
Foo<float> a;
Foo<int> b = a;
}
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Inlining the definition yields the correct error with GCC 9.3.0:
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main.cpp: In function 'int main()':
main.cpp:17:18: error: conversion from 'Foo<float>' to non-scalar type
'Foo<int>' requested
17 | Foo<int> b = a;
|
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