< cpp‎ | utility
Utilities library
Language support
Type support (basic types, RTTI)
Library feature-test macros (C++20)
Dynamic memory management
Program utilities
Coroutine support (C++20)
Variadic functions
Debugging support
Three-way comparison
General utilities
Date and time
Function objects
Formatting library (C++20)
Relational operators (deprecated in C++20)
Integer comparison functions
Swap and type operations
Common vocabulary types
Elementary string conversions

Defined in header <tuple>
template< class F, class Tuple >
constexpr decltype(auto) apply( F&& f, Tuple&& t );
(since C++17)
(until C++23)
template< class F, tuple-like Tuple >
constexpr decltype(auto) apply( F&& f, Tuple&& t ) noexcept(/* see below */);
(since C++23)

Invoke the Callable object f with the elements of t as arguments.

Given the exposition-only function apply-impl defined as follows: template<class F,class Tuple, std::size_t... I>
constexpr decltype(auto)
    apply-impl(F&& f, Tuple&& t, std::index_sequence<I...>) // exposition only
    return INVOKE(std::forward<F>(f), std::get<I>(std::forward<Tuple>(t))...);

The effect is equivalent to return apply-impl(std::forward<F>(f), std::forward<Tuple>(t),


[edit] Parameters

f - Callable object to be invoked
t - tuple whose elements to be used as arguments to f

[edit] Return value

The value returned by f.

[edit] Exceptions


(until C++23)
noexcept specification:  



where Is... denotes the parameter pack:

(since C++23)

[edit] 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 may be used.

(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)
Feature-test macro Value Std Feature
__cpp_lib_apply 201603L (C++17) std::apply

[edit] Example

#include <iostream>
#include <tuple>
#include <utility>
int add(int first, int second) { return first + second; }
template<typename T>
T add_generic(T first, T second) { return first + second; }
auto add_lambda = [](auto first, auto second) { return first + second; };
template<typename... Ts>
std::ostream& operator<<(std::ostream& os, std::tuple<Ts...> const& theTuple)
        [&os](Ts const&... tupleArgs)
            os << '[';
            std::size_t n{0};
            ((os << tupleArgs << (++n != sizeof...(Ts) ? ", " : "")), ...);
            os << ']';
        }, theTuple
    return os;
int main()
    // OK
    std::cout << std::apply(add, std::pair(1, 2)) << '\n';
    // Error: can't deduce the function type
    // std::cout << std::apply(add_generic, std::make_pair(2.0f, 3.0f)) << '\n'; 
    // OK
    std::cout << std::apply(add_lambda, std::pair(2.0f, 3.0f)) << '\n'; 
    // advanced example
    std::tuple myTuple{25, "Hello", 9.31f, 'c'};
    std::cout << myTuple << '\n';


[25, Hello, 9.31, c]

[edit] See also

creates a tuple object of the type defined by the argument types
(function template) [edit]
creates a tuple of forwarding references
(function template) [edit]
construct an object with a tuple of arguments
(function template) [edit]
invokes any Callable object with given arguments and possibility to specify return type(since C++23)
(function template) [edit]