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[/
Copyright 2019 Glen Joseph Fernandes
(glenjofe@gmail.com)
Distributed under the Boost Software License, Version 1.0.
(http://www.boost.org/LICENSE_1_0.txt)
]
[section:noinit_adaptor noinit_adaptor]
[simplesect Authors]
* Glen Fernandes
[endsimplesect]
[section Overview]
The header <boost/core/noinit_adaptor.hpp> provides the class
template `boost::noinit_adaptor` that converts any allocator into
one whose `construct(ptr)` performs default initialization via placement new,
and whose `destroy(ptr)` invokes `value_type` destructor directly.
[endsect]
[section Examples]
The following example shows use of this allocator adaptor to achieve default
initialization of elements of a trivial type, which are later assigned values.
```
#include <boost/core/noinit_adaptor.hpp>
#include <numeric>
#include <vector>
int main()
{
std::vector<int, boost::noinit_adaptor<std::allocator<int> > > v(5);
std::iota(v.begin(), v.end(), 1);
}
```
The `allocate_shared_noinit` function templates are now implemented simply
using `allocate_shared` with `noinit_adaptor`.
```
template<class T, class A>
enable_if_t<is_unbounded_array_v<T>, shared_ptr<T> >
allocate_shared_noinit(const A& a, size_t n)
{
return allocate_shared<T>(boost::noinit_adapt(a), n);
}
template<class T, class A>
enable_if_t<!is_unbounded_array_v<T>, shared_ptr<T> >
allocate_shared_noinit(const A& a)
{
return allocate_shared<T>(boost::noinit_adapt(a));
}
```
[endsect]
[section Reference]
```
namespace boost {
template<class A>
struct noinit_adaptor
: A {
template<class U>
struct rebind {
typedef noinit_adaptor<allocator_rebind_t<A, U> > other;
};
noinit_adaptor() noexcept;
template<class U>
noinit_adaptor(U&& u) noexcept;
template<class U>
noinit_adaptor(const noinit_adaptor<U>& u) noexcept;
template<class U>
void construct(U* p);
template<class U>
void destroy(U* p);
};
template<class T, class U>
bool operator==(const noinit_adaptor<T>& lhs,
const noinit_adaptor<U>& rhs) noexcept;
template<class T, class U>
bool operator!=(const noinit_adaptor<T>& lhs,
const noinit_adaptor<U>& rhs) noexcept;
template<class A>
noinit_adaptor<A> noinit_adapt(const A& a) noexcept;
} /* boost */
```
[section Constructors]
[variablelist
[[`noinit_adaptor() noexcept;`]
[[variablelist
[[Effects][Value initializes the A base class.]]]]]
[[`template<class U> noinit_adaptor(U&& u) noexcept;`]
[[variablelist
[[Requires][`A` shall be constructible from `U`.]]
[[Effects][Initializes the `A` base class with `std::forward<U>(u)`.]]]]]
[[`template<class U> noinit_adaptor(const noinit_adaptor<U>& u) noexcept;`]
[[variablelist
[[Requires][`A` shall be constructible from `U`.]]
[[Effects][Initializes the `A` base class with
`static_cast<const A&>(u)`.]]]]]]
[endsect]
[section Member functions]
[variablelist
[[`template<class U> void construct(U* p);`]
[[variablelist
[[Effects][`::new((void*)p) U`.]]]]]
[[`template<class U> void destroy(U* p);`]
[[variablelist
[[Effects][`p->~U()`.]]]]]]
[endsect]
[section Operators]
[variablelist
[[`template<class T, class U> constexpr bool
operator==(const noinit_adaptor<T>& lhs,
const noinit_adaptor<U>& rhs) noexcept;`]
[[variablelist
[[Returns][`static_cast<const T&>(lhs) == static_cast<const U&>(rhs)`.]]]]]
[[`template<class T, class U> constexpr bool
operator!=(const noinit_adaptor<T>& lhs,
const noinit_adaptor<U>& rhs) noexcept;`]
[[variablelist
[[Returns][`!(lhs == rhs)`.]]]]]]
[endsect]
[section Free functions]
[variablelist
[[`template<class A> noinit_adaptor<A> noinit_adapt(const A& a) noexcept;`]
[[variablelist
[[Returns][`noinit_adaptor<A>(a)`.]]]]]]
[endsect]
[endsect]
[endsect]
|
