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123 lines
3.4 KiB
C++
123 lines
3.4 KiB
C++
/**
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* \file libpmr/small_storage.h
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* \author mutouyun (orz@orzz.org)
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* \brief Unified SSO (Small Size Optimization) holder base.
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* \date 2023-09-02
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*/
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#pragma once
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#include <type_traits>
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#include <array>
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#include <typeinfo>
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#include <utility>
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#include <cstddef>
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#include "libimp/export.h"
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#include "libimp/construct.h"
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#include "libimp/byte.h"
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#include "libimp/generic.h"
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#include "libpmr/def.h"
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LIBPMR_NAMESPACE_BEG_
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class LIBIMP_EXPORT allocator;
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/**
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* \class holder_base
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* \brief Data holder base class.
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*/
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class holder_base {
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public:
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virtual ~holder_base() noexcept = default;
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virtual bool valid() const noexcept = 0;
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virtual std::type_info const &type() const noexcept = 0;
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virtual std::size_t sizeof_type() const noexcept = 0;
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virtual std::size_t count() const noexcept = 0;
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virtual std::size_t size () const noexcept = 0;
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virtual void *get() noexcept = 0;
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virtual void const *get() const noexcept = 0;
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virtual void move_to(allocator const &, void *) noexcept = 0;
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virtual void copy_to(allocator const &, void *) const noexcept(false) = 0;
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};
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/**
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* \class holder_null
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* \brief A holder implementation that does not hold any data objects.
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*/
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class holder_null : public holder_base {
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public:
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bool valid() const noexcept override { return false; }
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std::type_info const &type() const noexcept override { return typeid(nullptr);}
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std::size_t sizeof_type() const noexcept override { return 0; }
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std::size_t count() const noexcept override { return 0; }
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std::size_t size () const noexcept override { return 0; }
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void *get() noexcept override { return nullptr; }
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void const *get() const noexcept override { return nullptr; }
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/// \brief The passed destination pointer is never null,
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/// and the memory to which it points is uninitialized.
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void move_to(allocator const &, void *) noexcept override {}
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void copy_to(allocator const &, void *) const noexcept(false) override {}
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};
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template <typename Value, bool/*is on stack*/>
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class holder;
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/**
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* \class template <typename Value> holder<Value, true>
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* \brief A holder implementation that holds a data object if type `Value` on stack memory.
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* \tparam Value The storage type of the holder.
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*/
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template <typename Value>
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class holder<Value, true> : public holder_base {
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alignas(alignof(Value)) std::array<::LIBIMP::byte, sizeof(Value)> value_storage_;
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public:
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holder() = default; // uninitialized
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template <typename... A>
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holder(::LIBIMP::in_place_t, A &&...args) {
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::LIBIMP::construct<Value>(value_storage_.data(), std::forward<A>(args)...);
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}
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bool valid() const noexcept override {
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return true;
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}
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std::type_info const &type() const noexcept override {
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return typeid(Value);
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}
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std::size_t sizeof_type() const noexcept override {
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return sizeof(Value);
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}
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std::size_t count() const noexcept override {
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return 1;
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}
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std::size_t size() const noexcept override {
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return value_storage_.size();
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}
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void *get() noexcept override {
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return value_storage_.data();
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}
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void const *get() const noexcept override {
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return value_storage_.data();
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}
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void move_to(allocator const &, void *p) noexcept override {
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::LIBIMP::construct<holder>(p, ::LIBIMP::in_place, std::move(*static_cast<Value *>(get())));
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}
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void copy_to(allocator const &, void *p) const noexcept(false) override {
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::LIBIMP::construct<holder>(p, ::LIBIMP::in_place, *static_cast<Value *>(get()));
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}
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};
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LIBPMR_NAMESPACE_END_
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