How can constraints be imposed on types in template parameters in C++?

In C++, constraints on types in template parameters can be specified in several ways:

1. SFINAE (Substitution Failure Is Not An Error) — using std::enable_if and other metafunctions from <type_traits>, you can include or exclude template functions or classes based on type properties.

#include <type_traits>

template<typename T, typename = std::enable_if_t<std::is_integral_v<T>>>
void foo(T value) {
    // Implementation for integral types
}

int main() {
    foo(10);    // OK, int is integral
    // foo(3.14); // Compilation error, double is not suitable
}

2. Concepts — starting with C++20, concepts can be used for more readable and declarative type constraints.

#include <concepts>

template<std::integral T>
void foo(T value) {
    // Implementation for integral types
}

3. Static assertions (static_assert) — inside a template, you can check type properties and generate a compilation error with a message.

#include <type_traits>

template<typename T>
void foo(T value) {
    static_assert(std::is_integral_v<T>, "T must be an integral type");
    // ...
}

Thus, constraints help make templates safer and more understandable.