128 lines
3.1 KiB
C++
128 lines
3.1 KiB
C++
#ifndef optional_hh_INCLUDED
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#define optional_hh_INCLUDED
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#include "assert.hh"
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#include <utility>
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namespace Kakoune
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{
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template<typename T>
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struct Optional
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{
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public:
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constexpr Optional() : m_valid{false} {}
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Optional(const T& other) : m_valid{true} { new (&m_value) T(other); }
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Optional(T&& other) : m_valid{true} { new (&m_value) T(std::move(other)); }
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Optional(const Optional& other)
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: m_valid{other.m_valid}
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{
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if (m_valid)
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new (&m_value) T(other.m_value);
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}
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Optional(Optional&& other)
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noexcept(noexcept(new (nullptr) T(std::move(other.m_value))))
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: m_valid{other.m_valid}
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{
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if (m_valid)
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new (&m_value) T(std::move(other.m_value));
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}
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Optional& operator=(const Optional& other)
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{
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destruct_ifn();
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if ((m_valid = other.m_valid))
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new (&m_value) T(other.m_value);
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return *this;
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}
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Optional& operator=(Optional&& other)
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{
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destruct_ifn();
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if ((m_valid = other.m_valid))
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new (&m_value) T(std::move(other.m_value));
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return *this;
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}
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~Optional() { destruct_ifn(); }
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constexpr explicit operator bool() const noexcept { return m_valid; }
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bool operator==(const Optional& other) const
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{
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return m_valid == other.m_valid and
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(not m_valid or m_value == other.m_value);
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}
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bool operator!=(const Optional& other) const { return !(*this == other); }
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template<typename... Args>
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T& emplace(Args&&... args)
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{
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destruct_ifn();
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new (&m_value) T{std::forward<Args>(args)...};
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m_valid = true;
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return m_value;
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}
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T& operator*()
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{
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kak_assert(m_valid);
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return m_value;
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}
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const T& operator*() const { return *const_cast<Optional&>(*this); }
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T* operator->()
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{
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kak_assert(m_valid);
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return &m_value;
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}
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const T* operator->() const { return const_cast<Optional&>(*this).operator->(); }
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template<typename U> struct DecayOptionalImpl { using Type = U; };
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template<typename U> struct DecayOptionalImpl<Optional<U>> { using Type = typename DecayOptionalImpl<U>::Type; };
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template<typename U> using DecayOptional = typename DecayOptionalImpl<U>::Type;
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template<typename F>
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auto map(F f) -> Optional<DecayOptional<decltype(f(std::declval<T&&>()))>>
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{
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if (not m_valid)
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return {};
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return {f(m_value)};
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}
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template<typename U>
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auto cast() const -> Optional<U>
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{
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if (not m_valid)
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return {};
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return {(U)m_value};
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}
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template<typename U>
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T value_or(U&& fallback) const { return m_valid ? m_value : T{std::forward<U>(fallback)}; }
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template<typename U>
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T value_or_compute(U&& compute_func) const { return m_valid ? m_value : compute_func(); }
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void reset() { destruct_ifn(); m_valid = false; }
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private:
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void destruct_ifn() { if (m_valid) m_value.~T(); }
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struct Empty {};
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union
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{
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Empty m_empty; // disable default construction of value
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T m_value;
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};
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bool m_valid;
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};
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}
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#endif // optional_hh_INCLUDED
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