C++ function call Lambda expression: callback optimization for parameter passing and return value

In C, you can use Lambda expressions as function parameters to achieve the flexibility of callback functions. Specifically: Parameter passing: wrap the Lambda expression through std::function and pass it to the function in the form of a function pointer. Return value handling: Specify the return value type when declaring the callback function pointer using std::function. Practical case: Optimize callbacks in GUI event processing, avoid creating unnecessary objects or function pointers, and improve code simplicity and maintainability.

C function call Lambda expression: callback optimization of parameter passing and return value

In C, you can use Lambda expression as a parameter of function call , thereby achieving the flexibility of the callback function. This article will introduce how to pass Lambda expressions to functions, and show how to optimize the callback behavior of functions through practical cases.

Parameter passing

When a Lambda expression is passed as a function parameter, its syntax is as follows:

void foo(std::function<void(int)> callback) { callback(42); }

Among them, std::function<void(int)> Represents a function type that accepts an integer parameter and returns void.

Return value processing

When a Lambda expression is passed as a function parameter, it can also return a value. This can be achieved by using a callback function pointer of type std::function<ReturnType(Args...)>.

int bar(std::function<int(int, int)> callback) { 
    return callback(1, 2);
}

Practical case: Optimizing callbacks in event handling

Suppose we have a GUI application where each button click triggers a specific action. We can use lambda expressions to optimize callbacks in event handling to avoid unnecessary creation of object or function pointers.

Traditional method:

class Button {
    std::function<void()> callback;
public:
    Button(std::function<void()> callback) : callback(callback) {}
    void onClick() { callback(); }
};

Using Lambda expression optimization:

class Button {
public:
    void onClick(std::function<void()> callback) { callback(); }
};

In this optimized version, we can Pass the Lambda expression directly as a callback to the onClick() method. This not only reduces code redundancy but also improves readability and maintainability.

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