When and why is the return value stored on the stack, and when in the heap?

In Go, the return value can be stored either on the stack or on the heap, depending on where it is used and how long it lives.

• If the value is local and does not go beyond the function, it is usually placed on the stack — this is fast and efficient.
• If the value needs to be preserved after the function exits (for example, returning a pointer to a local variable), the compiler performs "escape analysis" and places such a value on the heap so that it is not destroyed after the function exits.

Example:

func foo() *int {
    x := 10
    return &x // x "escapes" to the heap to keep the pointer valid
}

func bar() int {
    y := 20
    return y // y is returned by value, stored on the stack
}

Thus, the decision on placement depends on the compiler analysis, which evaluates the lifetime of variables and the need to preserve them outside the current stack.