| operator() () | Function |
Function objects are objects with an operator() defined.
They are important for the effective use of the library. In the places
where one would expect to pass a pointer to a function to an algorithmic
template, the interface is specified to accept an object with an
operator()
defined. This not only makes algorithmic templates
work with pointers to functions, but also enables them to work with
arbitrary function objects. Using function objects together with function
templates increases the expressive power of the library as well as, making
the resulting code much more efficient. For example, to have a
by-element addition of two vectors
a and
b containing double and put the result into
a do:
transform (a.begin(), a.end(), b.begin(), a.begin(), plus());
To negate every element of a do:
transform (a.begin(), a.end(), a.begin(), negate());
| argument_type | Typedef on unary_function |
| result_type | Typedef on unary_function |
| first_argument_type | Typedef on binary_function |
| second_argument_type | Typedef on binary_function |
| result_type | Typedef on binary_function |
| The corresponding functions will inline the addition and the negation. To enable adaptors and other components to manipulate function objects that take one or two arguments it is required that they correspondingly provide typedefs argument_type and result_type for function objects that take one argument and first_argument_type, second_argument_type, and result_type for function objects that take two arguments. |
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