8. Callable Units

This chapter is intentionally not exhaustive

This book is about the C++ Standard library, therefore, will no go into the details of callable units. I provide only as much information as it’s necessary to use them correctly in the algorithms of the Standard Template Library. An exhaustive discussion of callable units should be part of a book about the C++ core language.

Many of the STL algorithms and containers can be parametrised with callable units or short callables. A callable is something that behaves like a function. Not only are these functions but also function objects and lambda functions. Predicates are special functions that return a boolean as the result. If a predicate has one argument, it’s called a unary predicate if a predicate has two arguments, it’s called a binary predicate. The same holds for functions. A function taking one argument is a unary function; a function taking two arguments is a binary function.

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