What is the practical use of the keyword defer?

The defer keyword in Go is used to postpone the execution of a function until the current function exits. This is convenient for guaranteed resource release, closing files, unlocking mutexes, and other cleanup operations.

Example:

func readFile(filename string) error {
    file, err := os.Open(filename)
    if err != nil {
        return err
    }
    defer file.Close() // the file will be closed when the function exits

    // work with the file
    // ...

    return nil
}

defer simplifies resource management and makes the code more readable and safe, preventing leaks.