make_unique

Introduction
Synopsis
Common Requirements
Free Functions
History

Introduction

The header file <boost/make_unique.hpp> provides overloaded function template make_unique for convenient creation of unique_ptr objects.

Synopsis

namespace boost {
    template<class U> // U is not array
    unique_ptr<U> make_unique();

#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
    template<class U, class... Args> // U is not array
    unique_ptr<U> make_unique(Args&&... args);
#endif

    template<class U> // U is not array
    unique_ptr<U> make_unique(U&& value);

    template<class U> // U is T[]
    unique_ptr<U> make_unique(size_t size);

    template<class U> // U is not array
    unique_ptr<U> make_unique_noinit();

    template<class U> // U is T[]
    unique_ptr<U> make_unique_noinit(size_t size);
}

Common Requirements

template<class U>
    unique_ptr<U> make_unique(args);
template<class U>
    unique_ptr<U> make_unique_noinit(args);

Effects: Allocates memory for an object of type U (or T[size] when U is T[], where size is determined from args as specified by the concrete overload). The object is initialized from args as specified by the concrete overload. If an exception is thrown, the functions have no effect.

Returns: A unique_ptr instance that stores and owns the address of the newly constructed object.

Postconditions: r.get() != 0, where r is the return value.

Throws: bad_alloc, or an exception thrown from the initialization of the object.

Remarks:

When an object of a non-array type T is specified to be initialized to a value value, or to T(list...), where list... is a list of constructor arguments, make_unique shall perform this initialization via the expression new T(value) or new T(list...) respectively.

When an object of type T is specified to be value-initialized, make_unique shall perform this initialization via the expression new T().

When an object of type T is specified to be default-initialized, make_unique_noinit shall perform this initialization via the expression new T.

Free Functions

template<class U, class... Args>
unique_ptr<U> make_unique(Args&&... args);

Returns: A unique_ptr to an object of type U, initialized to U(forward<Args>(args)...).

Remarks: This overload shall only participate in overload resolution when U is not an array type.

Examples:
unique_ptr<float> p1 = boost::make_unique<float>();
unique_ptr<point> p2 = boost::make_unique<point>(x, y);

template<class U>
unique_ptr<U> make_unique(U&& value);

Returns: A unique_ptr to an object of type U, initialized to move(value).

Remarks: This overload shall only participate in overload resolution when U is not an array type.

Examples:
unique_ptr<string> p1 = boost::make_unique<string>({'a', 'b'});
unique_ptr<point> p2 = boost::make_unique<point>({-10, 25});

template<class U>
unique_ptr<U> make_unique(size_t size);

Returns: A unique_ptr to a value-initialized object of type T[size].

Remarks: This overload shall only participate in overload resolution when U is of the form T[].

Examples:
unique_ptr<double[]> p1 = boost::make_unique<double[]>(4);
unique_ptr<int[][2]> p2 = boost::make_unique<int[][2]>(2);

template<class U>
unique_ptr<U> make_unique_noinit();

Returns: A unique_ptr to a default-initialized object of type U.

Remarks: This overload shall only participate in overload resolution when U is not an array type.

Examples:
unique_ptr<float> p1 = boost::make_unique_noinit<float>();
unique_ptr<point> p2 = boost::make_unique_noinit<point>();

template<class U>
unique_ptr<U> make_unique_noinit(size_t size);

Returns: A unique_ptr to a default-initialized object of type T[size].

Remarks: This overload shall only participate in overload resolution when U is of the form T[].

Examples:
unique_ptr<double[]> p1 = boost::make_unique_noinit<double[]>(4);
unique_ptr<int[][2]> p2 = boost::make_unique_noinit<int[][2]>(2);

History

January 2014. Glen Fernandes contributed implementations of make_unique for objects and arrays.

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