std::unary_function - cppreference.com (original) (raw)

| | | | | ------------------------------------------------------------------------------- | | ---------------------------------------- | | 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.

[edit] Member types

[edit] Example

#include #include #include #include   struct less_than_7 : std::unary_function<int, bool> { bool operator()(int i) const { return i < 7; } };   int main() { std::vector 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:

[edit] See also

| | copyable wrapper of any copy constructible callable object (class template) [edit] | | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | | move-only wrapper of any callable object that supports qualifiers in a given call signature (class template) [edit] | | | (deprecated in C++11)(removed in C++17) | creates an adaptor-compatible function object wrapper from a pointer to function (function template) [edit] | | (deprecated in C++11)(removed in C++17) | adaptor-compatible wrapper for a pointer to unary function (class template) [edit] | | (deprecated in C++11)(removed in C++17) | adaptor-compatible binary function base class (class template) [edit] |