eldritch horrors
3844e34053
sometimes it's useful to turn a box into a unique_ptr. let's have that. Change-Id: I3d142c6e157c5e61c16f3953b3b8b4cd616f0e93
127 lines
3.1 KiB
C++
127 lines
3.1 KiB
C++
#pragma once
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/// @file
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#include <concepts>
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#include <memory>
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#include <stdexcept>
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#include <type_traits>
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#include <assert.h>
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namespace nix {
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/** A pointer that's like Rust's Box: forwards comparisons to the inner class and is non-null */
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template<typename T>
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// FIXME: add custom deleter support
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class box_ptr
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{
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std::unique_ptr<T> inner;
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template<typename T2>
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friend class box_ptr;
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explicit box_ptr(std::unique_ptr<T> p)
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: inner(std::move(p))
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{
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assert(inner != nullptr);
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}
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public:
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using pointer = typename std::unique_ptr<T>::pointer;
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inline typename std::add_lvalue_reference<T>::type operator*() const noexcept
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{
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return *inner.get();
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}
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inline pointer operator->() const noexcept
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{
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return inner.get();
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}
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inline pointer get() const noexcept
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{
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return inner.get();
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}
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/**
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* Create a box_ptr from a nonnull unique_ptr.
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*/
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static inline box_ptr<T> unsafeFromNonnull(std::unique_ptr<T> p)
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{
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return box_ptr(std::move(p));
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}
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inline box_ptr<T> & operator=(box_ptr<T> && other) noexcept = default;
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// No copy for you.
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box_ptr<T> & operator=(const box_ptr<T> &) = delete;
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// XXX: we have to set the other's insides to nullptr, since we cannot
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// put a garbage object there, and we don't have any compiler
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// enforcement to not touch moved-from values. sighh.
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box_ptr(box_ptr<T> && other) = default;
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/** Conversion operator */
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template<typename Other>
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// n.b. the requirements here are the same as libstdc++ unique_ptr's checks but with concepts
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requires std::convertible_to<typename box_ptr<Other>::pointer, pointer> &&(!std::is_array_v<Other>)
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box_ptr(box_ptr<Other> && other) noexcept
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: inner(std::move(other.inner))
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{
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other.inner = nullptr;
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}
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box_ptr(box_ptr<T> & other) = delete;
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std::unique_ptr<T> take() &&
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{
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return std::move(inner);
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}
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};
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template<typename T>
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requires std::equality_comparable<T>
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bool operator==(box_ptr<T> const & x, box_ptr<T> const & y)
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{
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// Although there could be an optimization here that compares x == y, this
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// is unsound for floats with NaN, or anything else that violates
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// reflexivity.
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return *x == *y;
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}
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template<typename T>
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requires std::equality_comparable<T>
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bool operator!=(box_ptr<T> const & x, box_ptr<T> const & y)
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{
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return *x != *y;
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}
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#define MAKE_COMPARISON(OP) \
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template<typename T> \
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requires std::totally_ordered<T> \
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bool operator OP(box_ptr<T> const & x, box_ptr<T> const & y) \
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{ \
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return *x OP * y; \
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}
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MAKE_COMPARISON(<);
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MAKE_COMPARISON(>);
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MAKE_COMPARISON(>=);
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MAKE_COMPARISON(<=);
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#undef MAKE_COMPARISON
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template<typename T>
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requires std::three_way_comparable<T> std::compare_three_way_result_t<T, T>
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operator<=>(box_ptr<T> const & x, box_ptr<T> const & y)
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{
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return *x <=> *y;
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}
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template<typename T, typename... Args>
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inline box_ptr<T> make_box_ptr(Args &&... args)
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{
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return box_ptr<T>::unsafeFromNonnull(std::make_unique<T>(std::forward<Args>(args)...));
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}
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};
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