Adaptable Functors and Function Adapters
The predefined functors in Table 16.12 are all adaptable. Actually, the STL has five related concepts: adaptable generators, adaptable unary functions, adaptable binary functions, adaptable predicates, and adaptable binary predicates.
What makes a functor adaptable is that it carries typedef members identifying its argument types and return type. The members are called result_type, first_argument_type, and second_argument_type, and they represent what they sound like. For example, the return type of a plus<int> object is identified as plus<int>::result_type, and this would be a typedef for int.
The significance of a functor being adaptable is that it can then be used by function adapter objects, which ...
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