c++_mutable.md

Mutable Lambdas

Object captured by value in lambda are immutable by default. This is because operator() of the generated functional object (compiler generates functional object for lambdas) is const by default.

int a = 0;
auto lam = [a]() { ++a; }; // Compilation error

Using mutable keyword allows us to mutate objects captured by value.

int a = 0;
auto lam = [a]() mutable { ++a; };

The Parts Of Lambda

1. capture clause.
2. parameter list Optional.
3. mutable specification Optional.
4. exception specification Optional.
5. trailing-return-type Optional.
6. lambda body.