CompletionHandler

CompletionHandler is a programming concept, often found in languages like Swift, that allows for asynchronous operations to signal their completion and provide a result. It's essentially a closure or function that is passed as an argument to another function and is executed when that function has finished its task. This is particularly useful for operations that take time, such as network requests, file I/O, or complex computations, where blocking the main thread would lead to an unresponsive application.

When a function is called with a completion handler, it initiates the task. Once the task is done, either successfully with data or with an error, the completion handler is invoked. This handler typically receives the results of the operation as parameters. The code within the completion handler then executes, allowing the program to process the returned data or react to any errors. This pattern is a fundamental aspect of modern asynchronous programming, enabling responsive user interfaces and efficient execution of background tasks.

The use of completion handlers helps to manage the complexity of asynchronous code, making it more readable and maintainable compared to older callback-based approaches that could lead to deeply nested code. They are a cornerstone for building applications that perform operations without freezing the user interface, ensuring a smooth and fluid user experience.