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Use crazy magic and infer returned result type from return type of lambda.

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This commit is contained in:
Nerijus Arlauskas 2016-07-06 20:47:34 +03:00
parent 2cf23a45e4
commit 9b2c4842ae
3 changed files with 10 additions and 7 deletions
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4
src/maybe/result.hpp
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@ -193,8 +193,8 @@ namespace maybe {
return std::addressof(err_val);
}
template <typename R>
constexpr result<R, E> map(std::function<R(T v)> closure) noexcept;
template <typename F>
constexpr auto map(F f) noexcept -> maybe::result<decltype(f(std::declval<T>())), E>;
private:
constexpr void copy_from(const result<T, E>& other) noexcept;

11
src/maybe/result.inline.hpp
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@ -97,11 +97,14 @@ constexpr void maybe::result<T, E>::clear() noexcept
}
template <typename T, typename E>
template <typename R>
constexpr maybe::result<R, E> maybe::result<T, E>::map(std::function<R(T v)> closure) noexcept
template <typename F>
constexpr auto maybe::result<T, E>::map(F f) noexcept
-> maybe::result<decltype(f(std::declval<T>())), E>
{
typedef maybe::result<decltype(f(std::declval<T>())), E> return_result_t;
if (is_err()) {
return maybe::result<R, E>::err(err_value());
return return_result_t::err(std::forward<E>(err_value()));
}
return maybe::result<R, E>::ok(closure(ok_value()));
return return_result_t::ok(f(std::forward<T>(ok_value())));
};

2
tests/result_chaining_tests.cpp
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@ -21,7 +21,7 @@ TEST_CASE("result_chaining")
SECTION("converts result A to result B")
{
auto a = result<A, int>::ok(A("hello"));
auto b = a.map<B>([](const A& v) { return B(v.value); });
auto b = a.map([](A v) { return B(v.value); });
REQUIRE(b);
REQUIRE(b.ok_value().value == "hello");
}