How defer Works Internally in Go

Go's defer works by pushing a closure containing the deferred function and its captured arguments onto a stack at the moment the statement is executed, then popping and running those closures in Last-In-First-Out (LIFO) order when the surrounding function returns. The arguments are evaluated immediately when the defer statement runs, not when the function exits, ensuring the deferred logic executes with the values present at the deferral point.

func example() {
    x := 1
    defer func() { fmt.Println(x) }() // Prints 1, x evaluated now
    x = 2
} // Deferred function runs here in reverse order of deferral

Think of defer as a stack of sticky notes you write on as you work. You write the note (evaluate the arguments) immediately, but you don't read it until you are leaving the room (function returns). You read the notes in the exact reverse order you wrote them, ensuring the last thing you did is the first thing you clean up.