What is std::function and when to use it?

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**std::function** — type-erased callable wrapper. ```cpp // Stores any callable with matching signature std::function op; op = [](int a, int b) { return a + b; }; op = std::bind(std::plus{}, std::placeholders::_1, 2); int result = op(3, 4); // 7 ``` **vs templates:** ```cpp // Template: compile-time polymorphism (faster) template void call(F f) { f(); } // std::function: runtime polymorphism (flexible) void call(std::function f) { f(); } ``` **When to use:** - Storing callbacks - Function pointers in interfaces - When you need runtime flexibility - Avoid for performance-critical inner loops **Alternative:** Lambda with auto for zero-overhead.

C++: What is std::function and when to use it?