std::unary_function
From cppreference.com
< cpp | utility | functional
| Defined in header <functional>
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||
| template <typename ArgumentType, typename ResultType> struct unary_function; |
(deprecated) | |
unary_function is a base class for creating function objects with one argument.
unary_function does not define operator(); it is expected that derived classes will define this. unary_function provides only two types - argument_type and result_type - defined by the template parameters.
Some standard library function object adaptors, such as std::not1, require the function objects they adapt to have certain types defined; std::not1 requires the function object being adapted to have a type named argument_type. Deriving function objects that take one argument from unary_function is an easy way to make them compatible with those adaptors.
unary_function is deprecated in C++11. Its functionality has been made obsolete by std::function.
[edit] Member types
| Type | Definition |
| argument_type | ArgumentType |
| result_type | ResultType |
[edit] Example
#include <algorithm> #include <functional> #include <iostream> #include <vector> struct less_than_7 : std::unary_function<int, bool> { bool operator()(int i) const { return i < 7; } }; int main() { std::vector<int> v; for (int i = 0; i < 10; ++i) v.push_back(i); std::cout << std::count_if(v.begin(), v.end(), std::not1(less_than_7())); /* C++11 solution: // Cast to std::function<bool (int)> somehow - even with a lambda std::cout << std::count_if(v.begin(), v.end(), std::not1(std::function<bool (int)>([](int i){ return i < 7; })) ); */ }
Output:
3
[edit] See also
| (C++11) |
wraps callable object of any type with specified function call signature (class template) |
| (deprecated) |
creates an adaptor-compatible function object wrapper from a pointer to function (function template) |
| (deprecated) |
adaptor-compatible wrapper for a pointer to unary function (class template) |
| (deprecated) |
adaptor-compatible binary function base class (class template) |
