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142 lines
4.0 KiB
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142 lines
4.0 KiB
Plaintext
[/
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Copyright 2017 Glen Joseph Fernandes
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(glenjofe@gmail.com)
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Distributed under the Boost Software License, Version 1.0.
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(http://www.boost.org/LICENSE_1_0.txt)
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]
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[section:pointer_traits pointer_traits]
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[simplesect Authors]
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* Glen Fernandes
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[endsimplesect]
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[section Overview]
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The header <boost/core/pointer_traits.hpp> provides the class template
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`boost::pointer_traits` to facilitate use of pointer-like types. The C++11
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standard library introduced `std::pointer_traits` along with an allocator
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model which supported pointer-like types in addition to plain raw pointers.
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This implementation also supports C++98, and adds additional functionality
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for obtaining raw pointers from pointers.
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[endsect]
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[section Examples]
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The following function template obtains a raw pointer from a pointer and is
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well defined when the pointer aliases storage that has no object constructed
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in it.
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```
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template<class T>
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inline typename boost::pointer_traits<T>::element_type*
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to_raw_pointer(T v) noexcept
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{
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return boost::pointer_traits<T>::to_address(v);
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}
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```
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[endsect]
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[section Reference]
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```
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namespace boost {
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template<class T> struct pointer_traits {
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typedef T pointer;
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typedef ``['see below]`` element_type;
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typedef ``['see below]`` difference_type;
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template<class U> struct rebind_to { typedef ``['see below]`` type; };
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template<class U> using rebind = typename rebind_to<U>::type;
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static pointer pointer_to(``['see below]`` v);
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static element_type* to_address(pointer v) noexcept;
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};
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template<class T> struct pointer_traits<T*> {
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typedef T* pointer;
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typedef T element_type;
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typedef std::ptrdiff_t difference_type;
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template<class U> struct rebind_to { typedef U* type; };
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template<class U> using rebind = typename rebind_to<U>::type;
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static pointer pointer_to(``['see below]`` v) noexcept;
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static element_type* to_address(pointer v) noexcept;
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};
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}
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```
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[section Member types]
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[variablelist
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[[`typedef` ['see below] `element_type;`]
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[[variablelist
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[[Type]
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[`T::element_type` if such a type exists; otherwise `U` if `T` is a
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class template instantiation of the form `Pointer<U, Args>`, where
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`Args` is zero or more type arguments; otherwise the specialization
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is ill-formed.]]]]]
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[[`typedef` ['see below] `difference_type;`]
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[[variablelist
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[[Type]
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[`T::difference_type` if such a type exists; otherwise
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`std::ptrdiff_t`.]]]]]
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[[`template<class U> struct rebind_to { typedef` ['see below] `type; };`]
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[[variablelist
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[[Type]
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[`type` is `T::rebind<U>` if such a type exists; otherwise,
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`Pointer<V, Args>` if `T` is a class template instantiation of the
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form `Pointer<T, Args>`, where `Args` is zero or more type
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arguments; otherwise, the instantiation of `rebind_to` is
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ill-formed.]]]]]]
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[endsect]
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[section Member functions]
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[variablelist pointer_traits
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[[`static pointer pointer_to(`['see below] `v);`]
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[[variablelist
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[[Remark]
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[If `element_type` is a void type, the type of `v` is unspecified;
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otherwise, it is `element_type&`.]]
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[[Returns]
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[A pointer to `v` obtained by calling `T::pointer_to(v)`.]]]]]
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[[`static element_type* to_address(pointer v) noexcept;`]
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[[variablelist
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[[Requires]
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[`v` is not a null pointer.]]
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[[Returns]
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[A pointer of type `element_type*` that references the same location
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as the argument.]]]]]]
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[variablelist pointer_traits<T*>
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[[`static pointer pointer_to(`['see below] `v) noexcept;`]
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[[variablelist
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[[Remark]
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[If `element_type` is a void type, the type of `v` is unspecified;
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otherwise, it is `element_type&`.]]
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[[Returns]
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[The result of `std::addressof(v)`.]]]]]
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[[`static element_type* to_address(pointer v) noexcept;`]
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[[variablelist [[Returns] [The value of `v`.]]]]]]
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[endsect]
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[endsect]
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[section Acknowledgments]
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Glen Fernandes implemented `pointer_traits` with reviews and guidance from
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Peter Dimov.
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[endsect]
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[endsect]
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