if constexpr

`if constexpr` is a feature introduced in C++17. It allows compile-time branching based on a constant expression. It is used to conditionally compile code sections based on whether a certain condition is true or not at compile time. The code inside the `if constexpr` block is only compiled if the condition evaluates to true.

Unlike traditional `if` statements, where both branches are parsed and compiled regardless of the condition, `if constexpr` ensures that only the relevant branch is compiled. This can lead to improved performance and reduced code size in certain cases, as unnecessary code is eliminated during compilation.

Here's an example to illustrate its usage:

template <typename T>
void process(T value) {
    if constexpr (std::is_integral_v<T>) {
        // Code specific to integral types
        value += 10;
    } else {
        // Code for non-integral types
        value += 0.5;
    }
    
    // Rest of the code...
}

In this example, if the type `T` is an integral type, the code inside the `if constexpr` block will be compiled, and if it's not an integral type, the code inside the `else` block will be compiled. This allows for type-specific processing without incurring unnecessary code bloat.

I hope that answers your question! Let me know if you have any more.