Go-lang结构/作用域

Question

example code (edited code snippet): http://play.golang.org/p/eZV4WL-4N_

Why is it that

for x, _ := range body.Personality {
    body.Personality[x].Mutate()
}

successfully mutates the structs' contents, but

for _, pf := range body.Personality{
    pf.Mutate()
}

does not? Is it that range creates new instances of each item it iterates over? because the struct does in fact mutate but it doesn't persist.

Answer 1

The range keyword copies the results of the array, thus making it impossible to alter the contents using the value of range. You have to use the index or a slice of pointers instead of values if you want to alter the original array/slice.

This behaviour is covered by the spec as stated here. The crux is that an assignment line x := a[i] copies the value a[i] to x as it is no pointer. Since range is defined to use a[i], the values are copied.