C++

18.6    Literal Data Types: “constexpr” for Constructors

You already know constexpr, which allows you to tell the compiler to evaluate an expression at compile time. The precomputed value is then assigned to the variable:

constexpr int val = 2*12+3*6;  

In the program, the compiler will now directly insert 42 when you use val.

For methods and functions, constexpr means that, if possible, the function call is moved to compile time:

constexpr int add1(int v) { return v+1; }  

This means that if you write add1(5) or something similar in the source code, the compiler can directly write 6 into the compiled program, and nothing needs to happen at runtime.

It is something special when you provide a constructor with constexpr. Only then can you use the ...