988357696d
Summary: I was going to use this in some code I was working on but ended up not needing it. But it's useful nonetheless and I'm using it in a few places to replace reinterpret_cast. Pull Request resolved: https://github.com/facebook/rocksdb/pull/13648 Test Plan: existing tests, manually see compilation fail when pointed-to types are not same size integral types Reviewed By: cbi42 Differential Revision: D75576195 Pulled By: pdillinger fbshipit-source-id: e10c7a4959340f6f2b536de8088072a90e871fcf
99 lines
3.7 KiB
C++
99 lines
3.7 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#pragma once
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#include <initializer_list>
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#include <memory>
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#include <type_traits>
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#include "rocksdb/rocksdb_namespace.h"
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namespace ROCKSDB_NAMESPACE {
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// The helper function to assert the move from dynamic_cast<> to
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// static_cast<> is correct. This function is to deal with legacy code.
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// It is not recommended to add new code to issue class casting. The preferred
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// solution is to implement the functionality without a need of casting.
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template <class DestClass, class SrcClass>
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inline DestClass* static_cast_with_check(SrcClass* x) {
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DestClass* ret = static_cast<DestClass*>(x);
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#ifdef ROCKSDB_USE_RTTI
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assert(ret == dynamic_cast<DestClass*>(x));
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#endif
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return ret;
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}
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template <class DestClass, class SrcClass>
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inline std::shared_ptr<DestClass> static_cast_with_check(
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std::shared_ptr<SrcClass>&& x) {
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#if defined(ROCKSDB_USE_RTTI) && !defined(NDEBUG)
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auto orig_raw = x.get();
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#endif
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auto ret = std::static_pointer_cast<DestClass>(std::move(x));
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#if defined(ROCKSDB_USE_RTTI) && !defined(NDEBUG)
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assert(ret.get() == dynamic_cast<DestClass*>(orig_raw));
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#endif
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return ret;
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}
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// A wrapper around static_cast for lossless conversion between integral
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// types, including enum types, and pointers to such types. For example, this
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// can be used for converting between signed/unsigned or enum type and
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// underlying type without fear of stripping away data, now or in the future.
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template <typename To, typename From>
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inline To lossless_cast(From x) {
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using FromValue = typename std::remove_reference_t<From>;
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if constexpr (std::is_pointer_v<FromValue>) {
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static_assert(std::is_pointer_v<To>);
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using FromDeref = typename std::remove_pointer_t<FromValue>;
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using ToDeref = typename std::remove_pointer_t<To>;
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static_assert(std::is_integral_v<FromDeref> || std::is_enum_v<FromDeref>,
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"Only works on integral types");
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static_assert(std::is_integral_v<ToDeref> || std::is_enum_v<To>,
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"Only works on integral types");
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static_assert(sizeof(ToDeref) == sizeof(FromDeref), "Must be lossless");
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return reinterpret_cast<To>(x);
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} else {
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static_assert(std::is_integral_v<FromValue> || std::is_enum_v<FromValue>,
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"Only works on integral types");
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static_assert(std::is_integral_v<To> || std::is_enum_v<To>,
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"Only works on integral types");
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static_assert(sizeof(To) >= sizeof(FromValue), "Must be lossless");
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return static_cast<To>(x);
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}
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}
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// For disambiguating a potentially heterogeneous aggregate as a homogeneous
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// initializer list. E.g. might be able to write List({x, y}) in some cases
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// instead of std::vector<const Widget&>({x, y}).
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template <typename T>
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inline const std::initializer_list<T>& List(
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const std::initializer_list<T>& list) {
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return list;
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}
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// UnownedPtr<T> is useful as an efficient "optional reference" that can't
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// be accidentally converted to std::shared_ptr<T> nor std::unique_ptr<T>.
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template <typename T>
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class UnownedPtr {
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public:
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UnownedPtr() = default;
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UnownedPtr(std::nullptr_t) {}
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UnownedPtr(T* ptr) : ptr_(ptr) {}
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UnownedPtr(const UnownedPtr&) = default;
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UnownedPtr(UnownedPtr&&) = default;
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UnownedPtr& operator=(const UnownedPtr&) = default;
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UnownedPtr& operator=(UnownedPtr&&) = default;
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T* get() const { return ptr_; }
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T* operator->() const { return ptr_; }
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T& operator*() const { return *ptr_; }
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operator bool() const { return ptr_ != nullptr; }
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private:
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T* ptr_ = nullptr;
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};
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} // namespace ROCKSDB_NAMESPACE
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