what does T = 0 mean in a template parameter?

[JUANDENT]

What does T = 0 mean in the following code:

template<typename T, T = 0>
T moduloOf(T a, T b) {
    return a % b;
}

[mbozzi]

It makes a non-type template parameter of type T with a default value of 0.

C++17 introduced this alternative syntax:

template <auto T = 0>
T moduloOf(T a, T b) {
    return a % b;
}

[Peter87]

@mbozzi T is a type in the original code. In your code T isn't a type, but it's being used as a type, so the code doesn't compile.

[keskiverto]

template<typename T, T = 0>
T moduloOf(T a, T b) {
    return a % b;
}

The template takes one typename argument and one non-type argument.

auto answer1 = moduloOf<int>( 7, 3 );    // non-type has value 0
auto answer2 = moduloOf<int,42>( 7, 3 ); // non-type has value 42 

The non-type template parameter is unnamed and is not used anywhere in the templated function.


Does the "initialized with value 0" limit what type the T can be?
Similar to concepts in modern C++?