在Go中的结构成员或嵌入式结构上返回指针？

Question

Taking address and returning pointer to a local variable inside a function in Go causes compiler to allocate it on heap rather than stack, so that returned pointer remains valid.

Now what happens if I take and return address of a struct member or embedded struct ?

type A struct {
    a,b,c int
}
type B struct {
    A
    d,e,f int
}
func (b *B) get1() *A {
    return &b.A
}
func (b *B) get2() *A {
    localB := B{}
    return &localB.A
}

Will compiler allocate embedded struct A on heap and keep members of B on stack ?

Will garbage collector collect localB even if localB.A reference is still in use ?

How can compiler determine when to keep embedded struct on stack or heap in case if it's accessed through reflection ?

Answer 1

The compiler performs escape analysis to determine whether a variable may be used outside of the scope in which it is created, in which case it must be allocated on the heap. If the compiler can make sure that this won’t happen, it allocates the variable on the stack.

However, this is the current behaviour of the compiler, but it is not mentioned in the specification, so it may change in any future version.