leak.go

package main

// Demonstrates how taking the address of an embedded struct
// leaks the embedding struct's memory.

type Inner struct {
	x int
}

type Outer struct {
	b []byte
	i Inner
}

func foo() []*Inner {
	leak := true // Set to false if you don't want to leak.
	inners := []*Inner{}
	for i := 0; i < 500_000; i++ {
		if i%10_000 == 0 {
			println(i)
		}
		chunk := [1000_000]byte{0}
		o := Outer{b: chunk[:], i: Inner{x: 5}}
		if leak {
			// Keeps o (and thus chunk) alive.
			inners = append(inners, &o.i)
		} else {
			copy := o.i
			// The copy of o.i is not embedded in o, so it doesn't keep o alive.
			inners = append(inners, &copy)
		}
	}
	return inners
}

func main() {
	result := foo()
	println(len(result))
}