C.lambdas: Function objects and lambdas

• A function object is an object supplying an overloaded () so that you can call it.
• A lambda expression (colloquially often shortened to "a lambda") is a notation for generating a function object.
• Function objects should be cheap to copy (and therefore passed by value).

F.50: Use a lambda when a function won't do (to capture local variables, or to write a local function)

F.52: Prefer capturing by reference in lambdas that will be used locally, including passed to algorithms

F.53: Avoid capturing by reference in lambdas that will be used non-locally, including returned, stored on the heap, or passed to another thread

ES.28: Use lambdas for complex initialization, especially of const variables