functor base classes(3)
NAME
Functor Base Classes
Detailed Description
Function objects, or functors, are objects with an operator() defined
and accessible. They can be passed as arguments to algorithm templates
and used in place of a function pointer. Not only is the resulting
expressiveness of the library increased, but the generated code can be
more efficient than what you might write by hand. When we refer to
'functors,' then, generally we include function pointers in the
description as well.
Often, functors are only created as temporaries passed to algorithm
calls, rather than being created as named variables.
- Two examples taken from the standard itself follow. To perform a byelement addition of two vectors a and b containing double, and put the
result in a, use
- transform (a.begin(), a.end(), b.begin(), a.begin(), plus<double>());
- To negate every element in a, use
transform(a.begin(), a.end(), a.begin(), negate<double>());- The addition and negation functions will be inlined directly.
- The standard functors are derived from structs named unary_function and binary_function. These two classes contain nothing but typedefs, to aid in generic (template) programming. If you write your own functors, you might consider doing the same.
- Classes
- struct std::binary_function< _Arg1, _Arg2, _Result > struct std::unary_function< _Arg, _Result >