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Diffstat (limited to 'src/core/lib/support/manual_constructor.h')
-rw-r--r-- | src/core/lib/support/manual_constructor.h | 135 |
1 files changed, 135 insertions, 0 deletions
diff --git a/src/core/lib/support/manual_constructor.h b/src/core/lib/support/manual_constructor.h index d753cf98a0..fda7653dbc 100644 --- a/src/core/lib/support/manual_constructor.h +++ b/src/core/lib/support/manual_constructor.h @@ -22,12 +22,147 @@ // manually construct a region of memory with some type #include <stddef.h> +#include <stdlib.h> #include <new> #include <type_traits> #include <utility> +#include <grpc/support/log.h> + namespace grpc_core { +// this contains templated helpers needed to implement the ManualConstructors +// in this file. +namespace manual_ctor_impl { + +// is_one_of returns true it a class, Member, is present in a variadic list of +// classes, List. +template <class Member, class... List> +class is_one_of; + +template <class Member, class... List> +class is_one_of<Member, Member, List...> { + public: + static constexpr const bool value = true; +}; + +template <class Member, class A, class... List> +class is_one_of<Member, A, List...> { + public: + static constexpr const bool value = is_one_of<Member, List...>::value; +}; + +template <class Member> +class is_one_of<Member> { + public: + static constexpr const bool value = false; +}; + +// max_size_of returns sizeof(Type) for the largest type in the variadic list +// of classes, Types. +template <class... Types> +class max_size_of; + +template <class A> +class max_size_of<A> { + public: + static constexpr const size_t value = sizeof(A); +}; + +template <class A, class... B> +class max_size_of<A, B...> { + public: + static constexpr const size_t value = sizeof(A) > max_size_of<B...>::value + ? sizeof(A) + : max_size_of<B...>::value; +}; + +// max_size_of returns alignof(Type) for the largest type in the variadic list +// of classes, Types. +template <class... Types> +class max_align_of; + +template <class A> +class max_align_of<A> { + public: + static constexpr const size_t value = alignof(A); +}; + +template <class A, class... B> +class max_align_of<A, B...> { + public: + static constexpr const size_t value = alignof(A) > max_align_of<B...>::value + ? alignof(A) + : max_align_of<B...>::value; +}; + +} // namespace manual_ctor_impl + +template <class BaseType, class... DerivedTypes> +class PolymorphicManualConstructor { + public: + // No constructor or destructor because one of the most useful uses of + // this class is as part of a union, and members of a union could not have + // constructors or destructors till C++11. And, anyway, the whole point of + // this class is to bypass constructor and destructor. + + BaseType* get() { return reinterpret_cast<BaseType*>(&space_); } + const BaseType* get() const { + return reinterpret_cast<const BaseType*>(&space_); + } + + BaseType* operator->() { return get(); } + const BaseType* operator->() const { return get(); } + + BaseType& operator*() { return *get(); } + const BaseType& operator*() const { return *get(); } + + template <class DerivedType> + void Init() { + FinishInit(new (&space_) DerivedType); + } + + // Init() constructs the Type instance using the given arguments + // (which are forwarded to Type's constructor). + // + // Note that Init() with no arguments performs default-initialization, + // not zero-initialization (i.e it behaves the same as "new Type;", not + // "new Type();"), so it will leave non-class types uninitialized. + template <class DerivedType, typename... Ts> + void Init(Ts&&... args) { + FinishInit(new (&space_) DerivedType(std::forward<Ts>(args)...)); + } + + // Init() that is equivalent to copy and move construction. + // Enables usage like this: + // ManualConstructor<std::vector<int>> v; + // v.Init({1, 2, 3}); + template <class DerivedType> + void Init(const DerivedType& x) { + FinishInit(new (&space_) DerivedType(x)); + } + template <class DerivedType> + void Init(DerivedType&& x) { + FinishInit(new (&space_) DerivedType(std::move(x))); + } + + void Destroy() { get()->~BaseType(); } + + private: + template <class DerivedType> + void FinishInit(DerivedType* p) { + static_assert( + manual_ctor_impl::is_one_of<DerivedType, DerivedTypes...>::value, + "DerivedType must be one of the predeclared DerivedTypes"); + GPR_ASSERT(reinterpret_cast<BaseType*>(static_cast<DerivedType*>(p)) == p); + } + + typename std::aligned_storage< + grpc_core::manual_ctor_impl::max_size_of<DerivedTypes...>::value, + grpc_core::manual_ctor_impl::max_align_of<DerivedTypes...>::value>::type + space_; +}; + template <typename Type> class ManualConstructor { public: |