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License: MIT License
Example code and slides for my talk "std::variant and the Power of Pattern Matching"
License: MIT License
After the talk I suggested a downside to variants being complete, so extending a variant later (e.g. in the case of events). I came up with a possible solution:
namespace nonexhaustive_variant {
namespace detail {
template <class... T>
class nonexhaustive_variant {
struct P {};
public:
using type = std::variant<T..., P>;
};
} // namespace detail
template <class... T>
using nonexhaustive_variant = typename detail::nonexhaustive_variant<T...>::type;
} // namespace nonexhaustive_variant
using nonexhaustive_variant
forces users of match
to always provide a generic matcher:
struct A {};
struct B {};
using V = nonexhaustive_variant::nonexhaustive_variant<A, B>;
void foo(const V& v) {
match(v, //
[](const A&) { std::cout << "A" << std::endl; },
[](const B&) { std::cout << "B" << std::endl; },
[](const auto&) { std::cout << "???" << std::endl; });
}
Since the type P
is private since it cannot be matched explicitely. This allows extending V
in an interface without breaking all users of a library.
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