Trailing Return Type in C++ 11

The trailing return type syntax, a new method of indicating a function’s return type, was introduced in C++11.

Before C++11, the return type of a function was typically specified before the function name. However, in some cases, it could be challenging to express complex return types, especially when dealing with template functions or functions with decltype.

With the trailing return type syntax, you can specify the return type of a function after the parameter list using the auto keyword and the trailing -> arrow. This allows you to use expressions and decltype to deduce the return type based on the function’s implementation.

In the older format, it was necessary to specify the return type before the name of the function.

Syntax of Return Type before C++11

 function_return_type function_name(parameter_list){
     // Function implementation
    // ...
}

In the new syntax, auto keyword is written before the function name and the return type is specified after the function name and parameter list.

Syntax of Trailing Return Type

auto function_name(parameter_list) -> return_type {
    // Function implementation
    // ...
}

Example of Trailing Return Type

C++

// C++ Program to illustrate Trailing Return Type in C++ 11
#include <iostream>

// Trailing return type using auto and decltype
auto add(int a, int b) -> decltype(a + b) { return a + b; }

int main()
{
    int x = 5, y = 10;
    auto result = add(x, y);
    cout << "Result: " << result
              << endl; // Output: Result: 15
    return 0;
}

Output

Result: 15