Callable Objects
main.cpp
123456789101112131415161718192021#include <iostream> // Define a function object (functor) by creating a struct with operator() struct Multiplier { int factor; // Overload operator() to make this struct callable int operator()(int value) const { return value * factor; } }; int main() { Multiplier timesThree{3}; // Use the function object as a callable int result = timesThree(10); std::cout << "10 multiplied by 3 is " << result << std::endl; return 0; }
When working with callable objects in C++, you have several options: function objects (also called functors), lambdas, and function pointers. A function object is any object that can be called as if it were a function, which is achieved by overloading the operator() in a struct or class. This allows you to store state within the object, such as parameters or configuration, which is not possible with a regular function pointer.
A lambda is an anonymous function object that can capture variables from its surrounding scope, making it flexible and concise for short-lived operations. Lambdas are essentially compiler-generated function objects, which means they also can store state if needed.
A function pointer simply points to a function's address and allows you to call that function. However, function pointers cannot hold any state; they only reference existing functions and do not have the ability to capture or store data.
The primary distinction between these callable types lies in their ability to store state and their syntax. Functors and lambdas can both maintain state, while function pointers cannot. This makes function objects especially useful when you need a callable that remembers information between calls.
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main.cpp
123456789101112131415161718192021#include <iostream> // Define a function object (functor) by creating a struct with operator() struct Multiplier { int factor; // Overload operator() to make this struct callable int operator()(int value) const { return value * factor; } }; int main() { Multiplier timesThree{3}; // Use the function object as a callable int result = timesThree(10); std::cout << "10 multiplied by 3 is " << result << std::endl; return 0; }
When working with callable objects in C++, you have several options: function objects (also called functors), lambdas, and function pointers. A function object is any object that can be called as if it were a function, which is achieved by overloading the operator() in a struct or class. This allows you to store state within the object, such as parameters or configuration, which is not possible with a regular function pointer.
A lambda is an anonymous function object that can capture variables from its surrounding scope, making it flexible and concise for short-lived operations. Lambdas are essentially compiler-generated function objects, which means they also can store state if needed.
A function pointer simply points to a function's address and allows you to call that function. However, function pointers cannot hold any state; they only reference existing functions and do not have the ability to capture or store data.
The primary distinction between these callable types lies in their ability to store state and their syntax. Functors and lambdas can both maintain state, while function pointers cannot. This makes function objects especially useful when you need a callable that remembers information between calls.
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