Functors Overview

Philosophy

Functors (function objects) are callable objects that encapsulate operations. PrototypeSTL provides a complete set of comparators, arithmetic operations, and a type-erased function wrapper all working without exceptions or RTTI.

Categories

Category	Components	Header
Comparators	less, greater, equal_to, not_equal_to, less_equal, greater_equal	functors/comparators.hpp
Arithmetic	plus, minus, multiplies, divides, modulus, negate	functors/arithmetic.hpp
Logical	logical_and, logical_or, logical_not	functors/logical.hpp
Callable	function<Sig>	functors/function.hpp
Hashing	hash<T>	functors/hash.hpp

Usage Pattern

#include <prototype/functors/comparators.hpp>
#include <prototype/algorithms/sort.hpp>

prototype::vector<int> data = {5, 2, 8, 1};

// Sort descending using greater<> functor
prototype::sort(data.begin(), data.end(), prototype::greater<int>());

// Sort ascending (default)
prototype::sort(data.begin(), data.end(), prototype::less<int>());

Why Functors Over Function Pointers?

Feature	Function Pointer	Functor
Inlining	Rarely inlined	Always inlined
State	Cannot hold state	Can capture state
Optimization	Indirect call	Direct call (zero overhead)
Size	8 bytes (pointer)	1 byte (empty base optimization)

The compiler sees the functor type at the call site, enabling complete inlining. A function pointer creates an indirect call that blocks optimization.