std::make_from_tuple

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make_from_tuple
(C++17)
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Defined in header <tuple>
template < class T, class Tuple >
constexpr T make_from_tuple( Tuple&& t ) ;
(since C++17)
(until C++23)
template < class T, tuple-like Tuple >
constexpr T make_from_tuple( Tuple&& t ) ;
(since C++23)

Construct an object of type T, using the elements of the tuple t as the arguments to the constructor.

Given the exposition-only function /*make-from-tuple-impl*/ defined as follows:
template<class T, tuple-like Tuple, std::size_t... I > // no constraint on Tuple before C++23
constexpr T /*make-from-tuple-impl*/ (Tuple&& t, std::index_sequence <I...> )
{
return T(std:: get <I> ( std::forward <Tuple> (t) )...) ;
}

The effect is equivalent to:
return /*make-from-tuple-impl*/<T>(
std::forward <Tuple> (t)
std::make_index_sequence < std::tuple_size_v < std::remove_reference_t <Tuple>>> { }
);

If

(since C++23)

the program is ill-formed.

Parameters

t - tuple whose elements to be used as arguments to the constructor of T

Return value

The constructed T object or reference.

Notes

Tuple need not be std::tuple, and instead may be anything that supports std::get and std::tuple_size; in particular, std::array and std::pair

(until C++23)

Tuple is constrained to be tuple-like, i.e. each type therein is required to be a specialization of std::tuple or another type (such as std::array and std::pair) that models tuple-like

(since C++23)

Due to guaranteed copy elision, T need not be movable.

Feature-test macro Value Std Feature
__cpp_lib_make_from_tuple 201606L (C++17) std::make_from_tuple

Example

Run this code
#include <iostream>
#include <tuple>
 
struct Foo
{
    Foo(int first, float second, int third)
    {
        std::cout << first << ", " << second << ", " << third << '\n';
    }
};
 
int main()
{
    auto tuple = std::make_tuple(42, 3.14f, 0);
    std::make_from_tuple<Foo>(std::move(tuple));
}

Output: 

42, 3.14, 0

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3528 C++17 cast containing reinterpret_cast etc. was allowed in the case of 1-tuple prohibited

See also

(C++11)
 creates a tuple object of the type defined by the argument types
(function template)
(C++11)
 creates a tuple of forwarding references
(function template)
(C++17)
 calls a function with a tuple of arguments
(function template)
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