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[cpp2util] as: add constexpr branch for optionals #1062

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[cpp2util] as: add constexpr branch for optionals #1062

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12 changes: 12 additions & 0 deletions include/cpp2util.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1353,6 +1353,15 @@ auto as(X const& x CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT) -> decltype(auto) {
}
}

template<typename T>
struct is_optional : std::false_type {};

template<typename T>
struct is_optional<std::optional<T>> : std::true_type {};

template<typename T>
constexpr auto is_optional_v{is_optional<T>::value};

template< typename C, typename X >
auto as( X& x ) -> decltype(auto) {
if constexpr (std::is_same_v<C, X>) {
Expand All @@ -1364,6 +1373,9 @@ auto as( X& x ) -> decltype(auto) {
else if constexpr (std::is_base_of_v<X, C>) {
return Dynamic_cast<C&>(x);
}
else if constexpr (is_optional_v<X>) {
return x.value();
}
else {
return as<C>(std::as_const(x));
}
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