Tutorial by Examples

mutable modifier in this context is used to indicate that a data field of a const object may be modified without affecting the externally-visible state of the object. If you are thinking about caching a result of expensive computation, you should probably use this keyword. If you have a lock (for ...

By default, the implicit operator() of a lambda is const. This disallows performing non-const operations on the lambda. In order to allow modifying members, a lambda may be marked mutable, which makes the implicit operator() non-const: int a = 0; auto bad_counter = [a] { return a++; // er...