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std::make_unique, std::make_unique_default_init

Defined in header `<memory>`
template< class T, class... Args > unique_ptr<T> make_unique( Args&&... args );	(1)	(since C++14) (only for non-array types)
template< class T > unique_ptr<T> make_unique( std::size_t size );	(2)	(since C++14) (only for array types with unknown bound)
template< class T, class... Args > /* unspecified */ make_unique( Args&&... args ) = delete;	(3)	(since C++14) (only for array types with known bound)
template< class T > unique_ptr<T> make_unique_default_init( );	(4)	(since C++20) (only for non-array types)
template< class T > unique_ptr<T> make_unique_default_init( std::size_t size );	(5)	(since C++20) (only for array types with unknown bound)
template< class T, class... Args > /* unspecified */ make_unique_default_init( Args&&... args ) = delete;	(6)	(since C++20) (only for array types with known bound)

Constructs an object of type T and wraps it in a std::unique_ptr.

1) Constructs a non-array type T. The arguments args are passed to the constructor of T. This overload only participates in overload resolution if T is not an array type. The function is equivalent to:

unique_ptr<T>(new T(std::forward<Args>(args)...))

2) Constructs an array of unknown bound T. This overload only participates in overload resolution if T is an array of unknown bound. The function is equivalent to:

unique_ptr<T>(new typename std::remove_extent<T>::type[size]())

3,6) Construction of arrays of known bound is disallowed.

4) Same as (1), except that the object is default-initialized. This overload only participates in overload resolution if T is not an array type. The function is equivalent to:

unique_ptr<T>(new T)

5) Same as (2), except that the array is default-initialized. This overload only participates in overload resolution if T is an array of unknown bound. The function is equivalent to:

unique_ptr<T>(new typename std::remove_extent<T>::type[size])

Parameters

args	-	list of arguments with which an instance of `T` will be constructed.
size	-	the size of the array to construct

Return value

std::unique_ptr of an instance of type T.

Exceptions

May throw std::bad_alloc or any exception thrown by the constructor of T. If an exception is thrown, this function has no effect.

Possible Implementation

// note: this implementation does not disable this overload for array types
template<typename T, typename... Args>
std::unique_ptr<T> make_unique(Args&&... args)
{
    return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
}

Notes

Unlike std::make_shared (which has std::allocate_shared), std::make_unique does not have an allocator-aware counterpart. A hypothetical allocate_unique would be required to invent the deleter type D for the unique_ptr<T,D> it returns which would contain an allocator object and invoke both destroy and deallocate in its operator().

Example

#include <iostream>
#include <memory>
 
struct Vec3
{
    int x, y, z;
    Vec3() : x(0), y(0), z(0) { }
    Vec3(int x, int y, int z) :x(x), y(y), z(z) { }
    friend std::ostream& operator<<(std::ostream& os, Vec3& v) {
        return os << '{' << "x:" << v.x << " y:" << v.y << " z:" << v.z  << '}';
    }
};
 
int main()
{
    // Use the default constructor.
    std::unique_ptr<Vec3> v1 = std::make_unique<Vec3>();
    // Use the constructor that matches these arguments
    std::unique_ptr<Vec3> v2 = std::make_unique<Vec3>(0, 1, 2);
    // Create a unique_ptr to an array of 5 elements
    std::unique_ptr<Vec3[]> v3 = std::make_unique<Vec3[]>(5);
 
    std::cout << "make_unique<Vec3>():      " << *v1 << '\n'
              << "make_unique<Vec3>(0,1,2): " << *v2 << '\n'
              << "make_unique<Vec3[]>(5):   " << '\n';
    for (int i = 0; i < 5; i++) {
        std::cout << "     " << v3[i] << '\n';
    }
}

Output:

make_unique<Vec3>():      {x:0 y:0 z:0}
make_unique<Vec3>(0,1,2): {x:0 y:1 z:2}
make_unique<Vec3[]>(5):   
     {x:0 y:0 z:0}
     {x:0 y:0 z:0}
     {x:0 y:0 z:0}
     {x:0 y:0 z:0}
     {x:0 y:0 z:0}

(constructor)	constructs a new `unique_ptr` (public member function)
make_sharedmake_shared_default_init (C++20)	creates a shared pointer that manages a new object (function template)