C++ named requirements: Predicate
The Predicate requirements describe a callable that returns a value testable as a bool
.
Predicate is typically used with algorithms that take input data (individual objects/containers) and a predicate, which is then called on input data to decide on further course of action. Some examples of predicate usage in C++ standard library are:
-
std::all_of
,std::any_of
,std::none_of
Take an array of elements and a predicate as an input. Call predicate on individual input elements, and return true if for all/any/none elements, predicate returns true. -
std::find_if
Take sequence of elements, and a predicate. Return first element in the sequence, for which predicate returns value equal to true
In other words, if an algorithm takes a Predicate pred
and an iterator first
,
it should be able to test the object of the type pointed to by the iterator first
using the given predicate via a construct like if(pred(*first)) {...}
.
The function object pred
shall not apply any non-constant function through the dereferenced iterator and must accept a const object argument,
with the same behavior regardless of whether its argument is const or non-const (od C++20).
This function object may be a pointer to function or an object of a type with an appropriate function call operator.
Requirements
This section is incomplete
Reason: better describe actual requirements