Explain the use of Go's defer statement for scheduling function calls to be executed later?

In Go, the defer statement is used to schedule a function call to be executed just before the function it's declared in returns. This is often used for cleanup tasks or for tasks that need to be performed after a function has completed, regardless of whether an error occurred or not.

The **defer** statement can be used to schedule multiple function calls, and they are executed in a last-in, first-out (LIFO) order. This means that the most recently scheduled function call is executed first, and the first scheduled function call is executed last.

The **defer** statement can be useful in a number of situations, such as:

• Closing resources, such as files or network connections
• Unlocking mutexes or releasing other synchronization primitives
• Logging errors or other information
• Recovering from panics

Here is an example of using **defer** to close a file:

func readFile(filename string) ([]byte, error) {
    f, err := os.Open(filename)
    if err != nil {
        return nil, err
    }
    defer f.Close()

    return ioutil.ReadAll(f)
}

In this example, the **os.Open** function is used to open a file, and if an error occurs, it's returned immediately. If the file is successfully opened, a **defer** statement is used to schedule a call to the **Close** method on the file, which will be executed just before the function returns. Finally, the **ioutil.ReadAll** function is used to read the contents of the file and return them.

Using **defer** in this way ensures that the file will always be closed, even if an error occurs while reading the contents.