golang是否会复制整个接收者的值？

Question

I am almost sure of that but I want to be 100% sure. Because this seems weird after JS/PHP.

type Vertex struct {
    X, Y float64
}

func (v Vertex) Scale(f float64) {
    v.X = v.X * f
    v.Y = v.Y * f
}

So is it true that a deep copy (emphasize on this) of v Vertex parameter will be made on every Scale invocation? And therefore, we should use pointer receivers instead of value receivers in order to avoid the deep-copying?

And the same applies to parameters, right? What are other places where the copying happens?

Answer 1

Yes, a copy is made. Use pointer receivers if the value is large, you care about avoiding copies, and there are no other considerations (like wanting a copy for various reasons).

The Go FAQ has a useful entry on value vs. pointer receivers.

Note that a copy is made, but you say "deep copy" so be careful here - usually deep copy implies recursive copies including what pointers point to (like copying a whole tree). The copy here is a shallow copy. If Vertex has pointer fields, the values of these pointers will be copied, but not what they point to. There is plenty of discussion of shallow vs. deep copies in Go online; for example this SO question. If there are struct fields, the values of these will also be copied, so it's "deep" in the sense of struct nesting, but not "deep" in the sense of pointers.