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optional: add c++23 monadic interface

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This commit is contained in:
Michael Scire 2022-04-17 12:17:23 -07:00
parent dfba595cdc
commit 895b6d0470
1 changed files with 100 additions and 10 deletions
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110
libraries/libvapours/include/vapours/util/util_optional.hpp
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@ -32,6 +32,11 @@ namespace ams::util {
}
};
template<typename F>
struct OptionalFunction {
F &m_f;
};
}
struct nullopt_t {
@ -67,6 +72,9 @@ namespace ams::util {
template<typename V, typename... Args>
constexpr ALWAYS_INLINE StorageType(std::initializer_list<V> il, Args &&... args) : m_value(il, std::forward<Args>(args)...) { /* ... */ }
template<typename F, typename Arg>
constexpr ALWAYS_INLINE StorageType(OptionalFunction<F> f, Arg &&arg) : m_value(std::invoke(std::forward<F>(f.m_f), std::forward<Arg>(arg))) { /* ... */ }
};
template<typename U>
@ -82,6 +90,9 @@ namespace ams::util {
template<typename V, typename... Args>
constexpr ALWAYS_INLINE StorageType(std::initializer_list<V> il, Args &&... args) : m_value(il, std::forward<Args>(args)...) { /* ... */ }
template<typename F, typename Arg>
constexpr ALWAYS_INLINE StorageType(OptionalFunction<F> f, Arg &&arg) : m_value(std::invoke(std::forward<F>(f.m_f), std::forward<Arg>(arg))) { /* ... */ }
constexpr ALWAYS_INLINE ~StorageType() { /* ... */ }
};
@ -137,6 +148,12 @@ namespace ams::util {
std::destroy_at(std::addressof(m_payload.m_value));
}
template<typename F, typename Arg>
constexpr void Apply(impl::OptionalFunction<F> f, Arg &&arg) {
std::construct_at(std::addressof(m_payload), f, std::forward<Arg>(arg));
m_engaged = true;
}
constexpr ALWAYS_INLINE T &Get() { return m_payload.m_value; }
constexpr ALWAYS_INLINE const T &Get() const { return m_payload.m_value; }
@ -234,6 +251,11 @@ namespace ams::util {
constexpr void ResetImpl() { static_cast<Derived *>(this)->m_payload.Reset(); }
template<typename F, typename Arg>
constexpr void ApplyImpl(OptionalFunction<F> f, Arg &&arg) {
static_cast<Derived *>(this)->m_payload.Apply(f, std::forward<Arg>(arg));
}
constexpr ALWAYS_INLINE bool IsEngagedImpl() const { return static_cast<const Derived *>(this)->m_payload.m_engaged; }
constexpr ALWAYS_INLINE T &GetImpl() { return static_cast<Derived *>(this)->m_payload.Get(); }
@ -338,6 +360,11 @@ namespace ams::util {
std::is_assignable<T &, optional<U> &>::value ||
std::is_assignable<T &, const optional<U> &&>::value ||
std::is_assignable<T &, optional<U> &&>::value;
template<typename T>
constexpr inline bool IsOptional = false;
template<typename T>
constexpr inline bool IsOptional<optional<T>> = true;
}
@ -509,7 +536,80 @@ namespace ams::util {
return this->IsEngagedImpl() ? std::move(this->GetImpl()) : static_cast<T>(std::forward<U>(u));
}
template<typename F>
constexpr auto and_then(F &&f) & {
using U = typename std::remove_cvref<typename std::invoke_result<F, T &>::type>::type;
static_assert(impl::IsOptional<typename std::remove_cvref<U>::type>);
return this->IsEngagedImpl() ? std::invoke(std::forward<F>(f), **this) : U{};
}
template<typename F>
constexpr auto and_then(F &&f) const & {
using U = typename std::remove_cvref<typename std::invoke_result<F, const T &>::type>::type;
static_assert(impl::IsOptional<typename std::remove_cvref<U>::type>);
return this->IsEngagedImpl() ? std::invoke(std::forward<F>(f), **this) : U{};
}
template<typename F>
constexpr auto and_then(F &&f) && {
using U = typename std::remove_cvref<typename std::invoke_result<F, T>::type>::type;
static_assert(impl::IsOptional<typename std::remove_cvref<U>::type>);
return this->IsEngagedImpl() ? std::invoke(std::forward<F>(f), std::move(**this)) : U{};
}
template<typename F>
constexpr auto and_then(F &&f) const && {
using U = typename std::remove_cvref<typename std::invoke_result<F, const T>::type>::type;
static_assert(impl::IsOptional<typename std::remove_cvref<U>::type>);
return this->IsEngagedImpl() ? std::invoke(std::forward<F>(f), std::move(**this)) : U{};
}
template<typename F>
constexpr auto transform(F &&f) & {
using U = typename std::remove_cvref<typename std::invoke_result<F, T &>::type>::type;
return this->IsEngagedImpl() ? optional<U>(impl::OptionalFunction<F>{f}, **this) : optional<U>{};
}
template<typename F>
constexpr auto transform(F &&f) const & {
using U = typename std::remove_cvref<typename std::invoke_result<F, const T &>::type>::type;
return this->IsEngagedImpl() ? optional<U>(impl::OptionalFunction<F>{f}, **this) : optional<U>{};
}
template<typename F>
constexpr auto transform(F &&f) && {
using U = typename std::remove_cvref<typename std::invoke_result<F, T>::type>::type;
return this->IsEngagedImpl() ? optional<U>(impl::OptionalFunction<F>{f}, std::move(**this)) : optional<U>{};
}
template<typename F>
constexpr auto transform(F &&f) const && {
using U = typename std::remove_cvref<typename std::invoke_result<F, const T>::type>::type;
return this->IsEngagedImpl() ? optional<U>(impl::OptionalFunction<F>{f}, std::move(**this)) : optional<U>{};
}
template<typename F> requires std::invocable<F> && std::copy_constructible<T>
constexpr optional or_else(F &&f) const & {
using U = typename std::invoke_result<F>::type;
static_assert(std::same_as<typename std::remove_cvref_t<U>, optional>);
return this->IsEngagedImpl() ? *this : std::forward<F>(f)();
}
template<typename F> requires std::invocable<F> && std::move_constructible<T>
constexpr optional or_else(F &&f) && {
using U = typename std::invoke_result<F>::type;
static_assert(std::same_as<typename std::remove_cvref_t<U>, optional>);
return this->IsEngagedImpl() ? std::move(*this) : std::forward<F>(f)();
}
constexpr void reset() { this->ResetImpl(); }
private:
template<typename U> friend class optional;
template<typename F, typename Arg>
constexpr explicit optional(impl::OptionalFunction<F> f, Arg &&arg) {
this->ApplyImpl(f, std::forward<Arg>(arg));
}
};
namespace impl {
@ -588,16 +688,6 @@ namespace ams::util {
template<typename T, typename U>
constexpr inline impl::optional_ge_t<U, T> operator>=(const U &lhs, const optional<T> &rhs) { return !rhs || lhs >= *rhs; }
namespace impl {
template<typename T>
constexpr inline bool IsOptional = false;
template<typename T>
constexpr inline bool IsOptional<optional<T>> = true;
}
template<typename T, typename U> requires (!impl::IsOptional<U>) && std::three_way_comparable_with<T, U>
constexpr inline std::compare_three_way_result_t<T, U> operator<=>(const optional<T> &lhs, const U &rhs) {
return static_cast<bool>(lhs) ? *lhs <=> rhs : std::strong_ordering::less;