Function objects
Function objects are objects specifically designed to be used with a syntax similar to that of functions. In C++, this is achieved by defining member function operator() in their class, like for example:
struct myclass {
int operator()(int a) {return a;}
} myobject;
int x = myobject (0); // function-like syntax with object myobject |
They are especially useful as predicates or comparison functions to be used with standard algorithms.
The standard library provides standard definitions for several function objects and some ways to modify and adapt their behavior in header <functional>:
Base classes:
Operator classes
Arithmetic operations:
| plus | Addition function object class (class template) |
| minus | Subtraction function object class (class template) |
| multiplies | Multiplication function object class (class template) |
| divides | Division function object class (class template) |
| modulus | Modulus function object class (class template) |
| negate | Negative function object class (class template) |
Comparison operations:
| equal_to | Function object class for equality comparison (class template) |
| not_equal_to | Function object class for non-equality comparison (class template) |
| greater | Function object class for greater-than inequality comparison (class template) |
| less | Function object class for less-than inequality comparison (class template) |
| greater_equal | Function object class for greater-than-or-equal-to comparison (class template) |
| less_equal | Function object class for less-than-or-equal-to comparison (class template) |
Logical operations:
| logical_and | Logical AND function object class (class template) |
| logical_or | Logical OR function object class (class template) |
| logical_not | Logical NOT function object class (class template) |
Adaptor and conversion functions
Negators
| not1 | Return negation of unary function object (function template) |
| not2 | Return negation of binary function object (function template) |
Parameter binders
| bind1st | Return function object with first parameter binded (function template) |
| bind2nd | Return function object with second parameter binded (function template) |
Conversors
| ptr_fun | Convert function pointer to function object (function template) |
| mem_fun | Convert member function to function object (pointer version) (function template) |
| mem_fun_ref | Convert member function to function object (reference version) (class template) |
Instrumental types
| unary_negate | Generate negation of unary function object class (class template) |
| binary_negate | Generate negation of binary function object class (class template) |
| binder1st | Generate function object class with 1st parameter binded (class template) |
| binder2nd | Generate function object class with 2nd parameter binded (class template) |
| mem_fun_t | Generate function object class from parameterless member (pointer version) (class template) |
| mem_fun1_t | Generate function object class from single-parameter member (pointer version) (class template) |
| const_mem_fun_t | Generate function object class from const parameterless member (pointer version) (class template) |
| const_mem_fun1_t | Generate function object class from single-parameter const member (pointer version) (class template) |
| mem_fun_ref_t | Generate function object class from parameterless member (reference version) (class template) |
| mem_fun1_ref_t | Generate function object class from single-parameter member (reference version) (class template) |
| const_mem_fun_ref_t | Generate function object class from const parameterless member (reference version) (class template) |
| const_mem_fun1_ref_t | Generate function object class from single-parameter const member (reference version) (class template) |
