std::unary_function
From cppreference.com
| Defined in header <functional>
|
||
template< typename ArgumentType, typename ResultType >
struct unary_function;
|
(deprecated in C++11) (removed in C++17) |
|
std::unary_function is a base class for creating function objects with one argument.
std::unary_function does not define operator(); it is expected that derived classes will define this. std::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 std::unary_function is an easy way to make them compatible with those adaptors.
std::unary_function is deprecated in C++11.
Member types
| Type | Definition |
argument_type
|
ArgumentType
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result_type
|
ResultType
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Example
Run this code
#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(10, 7);
v[0] = v[1] = v[2] = 6;
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:
7