Concepts and Abbreviated Function Templates

You can use concepts with abbreviated function templates by placing the concept name before the auto keyword in the parameter declaration. This allows you to constrain the types deduced for the auto parameters. Here's an example:

1#include <concepts>
2#include <iostream>
3
4void printIntegral(std::integral auto value) {
5  std::cout << "Integral value: " << value;
6}
7
8int main() {
9  // Valid, int is an integral type
10  printIntegral(42);
11
12  // Invalid, double is not an integral type
13  printIntegral(3.14);
14}

1error: 'printIntegral': no matching overloaded function found
2could be 'void printIntegral(_T0)'
3the associated constraints are not satisfied
4the concept 'std::integral<double>' evaluated to false
5the constraint was not satisfied

In this example, the printIntegral function is an abbreviated function template that accepts a single parameter of an integral type. The std::integral concept is used before the auto keyword to constrain the deduced type.

Calling the function with an integral argument like 42 is valid, but calling it with a non-integral argument like 3.14 will result in a compilation error.