doc/smart_ptr/make_unique.adoc

////
Copyright 2017 Peter Dimov
Copyright 2017 Glen Joseph Fernandes (glenjofe@gmail.com)

Distributed under the Boost Software License, Version 1.0.

See accompanying file LICENSE_1_0.txt or copy at
http://www.boost.org/LICENSE_1_0.txt
////

[#make_unique]
# make_unique: Creating unique_ptr
:toc:
:toc-title:
:idprefix: make_unique_

## Description

The `make_unique` function templates provide convenient and safe ways to
create `std::unique_ptr` objects.

## Rationale

The {cpp}11 standard introduced `std::unique_ptr` but did not provide any
`make_unique` utility like `std::make_shared` that provided the same
exception safety and facility to avoid writing `new` expressions. Before it
was implemented by some standard library vendors (and prior to the {cpp}14
standard introducing `std::make_unique`), this library provided it due to
requests from users.

This library also provides additional overloads of `make_unique` for
default-initialization, when users do not need or want to incur the expense
of value-initialization. The {cpp} standard does not yet provide this
feature with `std::make_unique`.

## Synopsis

`make_unique` is defined in `<boost/smart_ptr/make_unique.hpp>`.

[subs=+quotes]
```
namespace boost {
  `// only if T is not an array type`
  template<class T, class... Args>
    std::unique_ptr<T> make_unique(Args&&... args);

  `// only if T is not an array type`
  template<class T>
    std::unique_ptr<T> make_unique(remove_reference_t<T>&& v);

  `// only if T is an array type of the form U[]`
  template<class T>
    std::unique_ptr<T> make_unique(std::size_t n);

  `// only if T is not an array type`
  template<class T>
    std::unique_ptr<T> make_unique_noinit();

  `// only if T is an array type of the form U[]`
  template<class T>
    std::unique_ptr<T> make_unique_noinit(std::size_t n);
}
```

## Free Functions

```
template<class T, class... Args>
  std::unique_ptr<T> make_unique(Args&&... args);
```
::
Remarks::: These overloads shall only participate in overload resolution when
`T` is not an array type.
Returns::: `std::unique_ptr<T>(new T(std::forward<Args>(args)\...)`.
Example::: `auto p = make_unique<int>();`

```
template<class T>
  std::unique_ptr<T> make_unique(remove_reference_t<T>&& v);
```
::
Remarks::: These overloads shall only participate in overload resolution when
`T` is not an array type.
Returns::: `std::unique_ptr<T>(new T(std::move(v))`.
Example::: `auto p = make_unique<std::vector<int> >({1, 2});`

```
template<class T>
  std::unique_ptr<T> make_unique(std::size_t n);
```
::
Remarks::: These overloads shall only participate in overload resolution when
`T` is an array type of the form `U[]`.
Returns::: `std::unique_ptr<U[]>(new U[n]())`.
Example::: `auto p = make_unique<double[]>(1024);`

```
template<class T>
  std::unique_ptr<T> make_unique_noinit();
```
::
Remarks::: These overloads shall only participate in overload resolution when
`T` is not an array type.
Returns::: `std::unique_ptr<T>(new T)`.
Example::: `auto p = make_unique_noinit<double[1024]>();`

```
template<class T>
  std::unique_ptr<T> make_unique_noinit(std::size_t n);
```
::
Remarks::: These overloads shall only participate in overload resolution when
`T` is an array type of the form `U[]`.
Returns::: `std::unique_ptr<U[]>(new U[n])`.
Example::: `auto p = make_unique_noinit<double[]>(1024);`