How Defer Works with Functions in Go

In Go, defer statements are executed in Last-In-First-Out (LIFO) order when the surrounding function returns. Arguments to deferred functions are evaluated immediately when the defer statement is encountered, not when the function actually runs.

func main() {
    x := 1
    defer func() { fmt.Println(x) }() // Prints 1 (evaluated now)
    x = 2
    defer func() { fmt.Println(x) }() // Prints 2 (evaluated now)
    // Execution order: second defer, then first defer
}

This means if you modify a variable after deferring a function that uses it, the deferred function will see the old value unless you capture the variable explicitly or defer a function that reads the variable at execution time.

Think of defer like stacking plates: the last one you put on the stack is the first one you take off. When you write a defer statement, Go immediately calculates the values for any arguments you pass, so if you change a variable later, the deferred function won't see the new value unless you tell it to check again when it runs.