349 lines
12 KiB
C++
349 lines
12 KiB
C++
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///////////////////////////////////////////////////////////////////////////////
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//
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// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
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//
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// This code is licensed under the MIT License (MIT).
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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// THE SOFTWARE.
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//
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///////////////////////////////////////////////////////////////////////////////
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#ifndef GSL_POINTERS_H
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#define GSL_POINTERS_H
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#include "assert" // for Ensures, Expects
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#include <algorithm> // for forward
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#include <cstddef> // for ptrdiff_t, nullptr_t, size_t
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#include <memory> // for shared_ptr, unique_ptr
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#include <system_error> // for hash
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#include <type_traits> // for enable_if_t, is_convertible, is_assignable
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#include <utility> // for declval
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#if !defined(GSL_NO_IOSTREAMS)
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#include <iosfwd> // for ostream
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#endif // !defined(GSL_NO_IOSTREAMS)
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namespace gsl
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{
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namespace details
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{
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template <typename T, typename = void>
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struct is_comparable_to_nullptr : std::false_type
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{
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};
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template <typename T>
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struct is_comparable_to_nullptr<
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T,
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std::enable_if_t<std::is_convertible<decltype(std::declval<T>() != nullptr), bool>::value>>
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: std::true_type
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{
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};
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// Resolves to the more efficient of `const T` or `const T&`, in the context of returning a const-qualified value
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// of type T.
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//
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// Copied from cppfront's implementation of the CppCoreGuidelines F.16 (https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rf-in)
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template<typename T>
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using value_or_reference_return_t = std::conditional_t<
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sizeof(T) < 2*sizeof(void*) && std::is_trivially_copy_constructible<T>::value,
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const T,
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const T&>;
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} // namespace details
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//
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// GSL.owner: ownership pointers
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//
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using std::shared_ptr;
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using std::unique_ptr;
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//
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// owner
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//
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// `gsl::owner<T>` is designed as a safety mechanism for code that must deal directly with raw pointers that own memory.
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// Ideally such code should be restricted to the implementation of low-level abstractions. `gsl::owner` can also be used
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// as a stepping point in converting legacy code to use more modern RAII constructs, such as smart pointers.
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//
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// T must be a pointer type
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// - disallow construction from any type other than pointer type
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//
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template <class T, class = std::enable_if_t<std::is_pointer<T>::value>>
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using owner = T;
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//
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// not_null
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//
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// Restricts a pointer or smart pointer to only hold non-null values.
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//
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// Has zero size overhead over T.
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//
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// If T is a pointer (i.e. T == U*) then
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// - allow construction from U*
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// - disallow construction from nullptr_t
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// - disallow default construction
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// - ensure construction from null U* fails
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// - allow implicit conversion to U*
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//
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template <class T>
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class not_null
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{
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public:
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static_assert(details::is_comparable_to_nullptr<T>::value, "T cannot be compared to nullptr.");
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template <typename U, typename = std::enable_if_t<std::is_convertible<U, T>::value>>
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constexpr not_null(U&& u) noexcept(std::is_nothrow_move_constructible<T>::value) : ptr_(std::forward<U>(u))
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{
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Expects(ptr_ != nullptr);
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}
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template <typename = std::enable_if_t<!std::is_same<std::nullptr_t, T>::value>>
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constexpr not_null(T u) noexcept(std::is_nothrow_move_constructible<T>::value) : ptr_(std::move(u))
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{
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Expects(ptr_ != nullptr);
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}
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template <typename U, typename = std::enable_if_t<std::is_convertible<U, T>::value>>
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constexpr not_null(const not_null<U>& other) noexcept(std::is_nothrow_move_constructible<T>::value) : not_null(other.get())
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{}
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not_null(const not_null& other) = default;
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not_null& operator=(const not_null& other) = default;
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constexpr details::value_or_reference_return_t<T> get() const
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noexcept(noexcept(details::value_or_reference_return_t<T>{std::declval<T&>()}))
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{
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return ptr_;
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}
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constexpr operator T() const { return get(); }
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constexpr decltype(auto) operator->() const { return get(); }
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constexpr decltype(auto) operator*() const { return *get(); }
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// prevents compilation when someone attempts to assign a null pointer constant
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not_null(std::nullptr_t) = delete;
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not_null& operator=(std::nullptr_t) = delete;
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// unwanted operators...pointers only point to single objects!
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not_null& operator++() = delete;
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not_null& operator--() = delete;
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not_null operator++(int) = delete;
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not_null operator--(int) = delete;
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not_null& operator+=(std::ptrdiff_t) = delete;
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not_null& operator-=(std::ptrdiff_t) = delete;
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void operator[](std::ptrdiff_t) const = delete;
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private:
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T ptr_;
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};
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template <class T>
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auto make_not_null(T&& t) noexcept
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{
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return not_null<std::remove_cv_t<std::remove_reference_t<T>>>{std::forward<T>(t)};
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}
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#if !defined(GSL_NO_IOSTREAMS)
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template <class T>
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std::ostream& operator<<(std::ostream& os, const not_null<T>& val)
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{
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os << val.get();
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return os;
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}
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#endif // !defined(GSL_NO_IOSTREAMS)
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template <class T, class U>
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auto operator==(const not_null<T>& lhs,
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const not_null<U>& rhs) noexcept(noexcept(lhs.get() == rhs.get()))
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-> decltype(lhs.get() == rhs.get())
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{
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return lhs.get() == rhs.get();
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}
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template <class T, class U>
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auto operator!=(const not_null<T>& lhs,
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const not_null<U>& rhs) noexcept(noexcept(lhs.get() != rhs.get()))
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-> decltype(lhs.get() != rhs.get())
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{
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return lhs.get() != rhs.get();
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}
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template <class T, class U>
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auto operator<(const not_null<T>& lhs,
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const not_null<U>& rhs) noexcept(noexcept(std::less<>{}(lhs.get(), rhs.get())))
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-> decltype(std::less<>{}(lhs.get(), rhs.get()))
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{
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return std::less<>{}(lhs.get(), rhs.get());
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}
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template <class T, class U>
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auto operator<=(const not_null<T>& lhs,
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const not_null<U>& rhs) noexcept(noexcept(std::less_equal<>{}(lhs.get(), rhs.get())))
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-> decltype(std::less_equal<>{}(lhs.get(), rhs.get()))
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{
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return std::less_equal<>{}(lhs.get(), rhs.get());
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}
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template <class T, class U>
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auto operator>(const not_null<T>& lhs,
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const not_null<U>& rhs) noexcept(noexcept(std::greater<>{}(lhs.get(), rhs.get())))
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-> decltype(std::greater<>{}(lhs.get(), rhs.get()))
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{
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return std::greater<>{}(lhs.get(), rhs.get());
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}
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template <class T, class U>
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auto operator>=(const not_null<T>& lhs,
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const not_null<U>& rhs) noexcept(noexcept(std::greater_equal<>{}(lhs.get(), rhs.get())))
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-> decltype(std::greater_equal<>{}(lhs.get(), rhs.get()))
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{
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return std::greater_equal<>{}(lhs.get(), rhs.get());
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}
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// more unwanted operators
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template <class T, class U>
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std::ptrdiff_t operator-(const not_null<T>&, const not_null<U>&) = delete;
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template <class T>
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not_null<T> operator-(const not_null<T>&, std::ptrdiff_t) = delete;
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template <class T>
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not_null<T> operator+(const not_null<T>&, std::ptrdiff_t) = delete;
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template <class T>
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not_null<T> operator+(std::ptrdiff_t, const not_null<T>&) = delete;
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template <class T, class U = decltype(std::declval<const T&>().get()), bool = std::is_default_constructible<std::hash<U>>::value>
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struct not_null_hash
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{
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std::size_t operator()(const T& value) const { return std::hash<U>{}(value.get()); }
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};
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template <class T, class U>
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struct not_null_hash<T, U, false>
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{
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not_null_hash() = delete;
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not_null_hash(const not_null_hash&) = delete;
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not_null_hash& operator=(const not_null_hash&) = delete;
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};
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} // namespace gsl
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namespace std
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{
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template <class T>
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struct hash<gsl::not_null<T>> : gsl::not_null_hash<gsl::not_null<T>>
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{
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};
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} // namespace std
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namespace gsl
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{
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//
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// strict_not_null
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//
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// Restricts a pointer or smart pointer to only hold non-null values,
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//
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// - provides a strict (i.e. explicit constructor from T) wrapper of not_null
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// - to be used for new code that wishes the design to be cleaner and make not_null
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// checks intentional, or in old code that would like to make the transition.
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//
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// To make the transition from not_null, incrementally replace not_null
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// by strict_not_null and fix compilation errors
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//
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// Expect to
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// - remove all unneeded conversions from raw pointer to not_null and back
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// - make API clear by specifying not_null in parameters where needed
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// - remove unnecessary asserts
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//
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template <class T>
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class strict_not_null : public not_null<T>
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{
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public:
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template <typename U, typename = std::enable_if_t<std::is_convertible<U, T>::value>>
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constexpr explicit strict_not_null(U&& u) : not_null<T>(std::forward<U>(u))
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{}
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template <typename = std::enable_if_t<!std::is_same<std::nullptr_t, T>::value>>
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constexpr explicit strict_not_null(T u) : not_null<T>(u)
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{}
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template <typename U, typename = std::enable_if_t<std::is_convertible<U, T>::value>>
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constexpr strict_not_null(const not_null<U>& other) : not_null<T>(other)
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{}
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template <typename U, typename = std::enable_if_t<std::is_convertible<U, T>::value>>
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constexpr strict_not_null(const strict_not_null<U>& other) : not_null<T>(other)
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{}
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// To avoid invalidating the "not null" invariant, the contained pointer is actually copied
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// instead of moved. If it is a custom pointer, its constructor could in theory throw exceptions.
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strict_not_null(strict_not_null&& other) noexcept(std::is_nothrow_copy_constructible<T>::value) = default;
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strict_not_null(const strict_not_null& other) = default;
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strict_not_null& operator=(const strict_not_null& other) = default;
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strict_not_null& operator=(const not_null<T>& other)
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{
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not_null<T>::operator=(other);
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return *this;
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}
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// prevents compilation when someone attempts to assign a null pointer constant
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strict_not_null(std::nullptr_t) = delete;
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strict_not_null& operator=(std::nullptr_t) = delete;
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// unwanted operators...pointers only point to single objects!
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strict_not_null& operator++() = delete;
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strict_not_null& operator--() = delete;
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strict_not_null operator++(int) = delete;
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strict_not_null operator--(int) = delete;
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strict_not_null& operator+=(std::ptrdiff_t) = delete;
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strict_not_null& operator-=(std::ptrdiff_t) = delete;
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void operator[](std::ptrdiff_t) const = delete;
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};
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// more unwanted operators
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template <class T, class U>
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std::ptrdiff_t operator-(const strict_not_null<T>&, const strict_not_null<U>&) = delete;
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template <class T>
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strict_not_null<T> operator-(const strict_not_null<T>&, std::ptrdiff_t) = delete;
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template <class T>
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strict_not_null<T> operator+(const strict_not_null<T>&, std::ptrdiff_t) = delete;
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template <class T>
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strict_not_null<T> operator+(std::ptrdiff_t, const strict_not_null<T>&) = delete;
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template <class T>
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auto make_strict_not_null(T&& t) noexcept
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{
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return strict_not_null<std::remove_cv_t<std::remove_reference_t<T>>>{std::forward<T>(t)};
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}
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#if (defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L))
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// deduction guides to prevent the ctad-maybe-unsupported warning
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template <class T>
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not_null(T) -> not_null<T>;
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template <class T>
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strict_not_null(T) -> strict_not_null<T>;
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#endif // ( defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L) )
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} // namespace gsl
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namespace std
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{
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template <class T>
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struct hash<gsl::strict_not_null<T>> : gsl::not_null_hash<gsl::strict_not_null<T>>
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{
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};
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} // namespace std
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#endif // GSL_POINTERS_H
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