What higher-order functions have you used in your projects, and can you provide examples of their application?

In iOS development, higher-order functions are often used for processing collections and managing asynchronous operations. For example, methods like map, filter, and reduce are higher-order functions that accept other functions as arguments.

An example of using map to transform an array of numbers:

let numbers = [1, 2, 3, 4, 5]
let squaredNumbers = numbers.map { $0 * $0 }
print(squaredNumbers) // [1, 4, 9, 16, 25]

Closures are also frequently passed to functions for handling events or asynchronous operations:

func fetchData(completion: (Result<String, Error>) -> Void) {
    // Simulate asynchronous data loading
    DispatchQueue.global().async {
        let data = "Data"
        completion(.success(data))
    }
}

fetchData { result in
    switch result {
    case .success(let data):
        print("Received: \(data)")
    case .failure(let error):
        print("Error: \(error)")
    }
}

Thus, higher-order functions allow writing more expressive and concise code.