Lambda Functions in C++

A lambda function, or simply "lambda", is an anonymous (unnamed) function that is defined in place, within your source code, and with a concise syntax. Lambda functions were introduced in C++11 and have since become a widely used feature, especially in combination with the Standard Library algorithms.

Syntax

Here is a basic syntax of a lambda function in C++:

[capture-list](parameters) -> return_type {
    // function body
};

capture-list: A list of variables from the surrounding scope that the lambda function can access.
parameters: The list of input parameters, just like in a regular function. Optional.
return_type: The type of the value that the lambda function will return. This part is optional, and the compiler can deduce it in many cases.
function body: The code that defines the operation of the lambda function.

Usage Examples

Here are a few examples to demonstrate the use of lambda functions in C++:

Lambda function with no capture, parameters, or return type.

auto printHello = []() {
    std::cout << "Hello, World!\n";
};
printHello(); // Output: Hello, World!

Lambda function with parameters.

auto add = [](int a, int b) {
    return a + b;
};
int result = add(3, 4); // result = 7

Lambda function with capture-by-value.

int multiplier = 3;
auto times = [multiplier](int a) {
    return a * multiplier;
};
int result = times(5); // result = 15

Lambda function with capture-by-reference.

int expiresInDays = 45;
auto updateDays = [&expiresInDays](int newDays) {
    expiresInDays = newDays;
};
updateDays(30); // expiresInDays = 30

Note that, when using the capture by reference, any change made to the captured variable inside the lambda function will affect its value in the surrounding scope.

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