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Tip of the Day
Language: C++
Expertise: Advanced
Dec 19, 2000



Building the Right Environment to Support AI, Machine Learning and Deep Learning

Function Object Bases

To simplify the process of writing custom function objects, the Standard Library provides two classes that serve as base classes of such objects: std::unary_function and std::binary_function. Both are declared in the header <functional>. As the names suggest, unary_function serves as the base of function objects taking one argument and binary_function serves as the base of function objects taking two arguments. Here's the definition of these base classes:
template  struct unary_function {
 typedef Arg argument_type;
 typedef Res result_type;
template  struct
 binary_function {
 typedef Arg first_argument_type;
 typedef Arg2 second_argument_type;
 typedef Res result_type;

These classes don't provide any useful functionality. They are used to ensure that arguments and return values have uniform names. In the following example, a predicate (a function object returning bool) called is_vowel, which takes one argument, inherits from unary_function:
class is_vowel: public unary_function
 bool operator ()(T t) const
  if ((t=='a')||(t=='e')||(t=='i')||(t=='o')||(t=='u'))
   return true;
  return false;
Danny Kalev
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