C++ Tuple::forward_as_tuple() Function

The C++ std::tuple::forward_as_tuple() function is used to construct a tuple by fowarding its arguments, preserving their original types and forwarding them as rvalue references. unlike the std::make_tuple() function, it maintains the value category of each element.

This function can be used in conjunction with functions like std::tie() and std::tuple_cat() to manipulate tuples and unpack their elements.

Syntax

Following is the syntax for std::tuple::forward_as_tuple() function.

 forward_as_tuple (Types&&... args) noexcept; 

Parameters

• args − It indicates the list of elements to be forwarded as a tuple object of reference.

Example

Let's look at the following example, where we are going to use the forward_as_tuple() function to create a tuple of references to x and y and then passed to print the tuple elements.

 #include <tuple> #include <iostream> void tp(const std::tuple<int, float>& t) { std::cout << std::get<0>(t) << ", " << std::get<1>(t) << " " <<std::endl; } int main() { int x = 2; float y =0.02; tp(std::forward_as_tuple(x, y)); return 0; } 

Output

Let us compile and run the above program, this will produce the following result −

 2, 0.02 

Example

Consider the following example, where we are going to return the multiple values from the function.

 #include <tuple> #include <iostream> std::tuple<float, std::string> get_values() { float a = 0.01; std::string b = "TutorialsPoint"; return std::forward_as_tuple(a, b); } int main() { auto x = get_values(); std::cout << std::get<0>(x) << ", " << std::get<1>(x) << std::endl; return 0; } 

Output

Following is the output of the above code −

 0.01, TutorialsPoint 

Example

In the following example, we are going to use the std::tie() with the forward_as_tuple() function.

 #include <tuple> #include <iostream> int main() { int x = 1; float y = 0.01; std::tie(x, y) = std::forward_as_tuple(x, y); std::cout << x << ", " << y << std::endl; return 0; } 

Output

If we run the above code it will generate the following output −

 1, 0.01 

Example

Following is the example, where we are going to use the forward_as_tuple() function along with std::apply().

 #include <tuple> #include <iostream> void a(int x, const std::string& y) { std::cout << x << ", " << y << std::endl; } int main() { auto b = std::forward_as_tuple(123, "Welcome"); std::apply(a, b); return 0; } 

Output

Output of the above code is as follows −

 123, Welcome