Go update slice iterating error “does not support indexing”

Question

I\'m trying to iterate through slice values and update one or more values, accessing it by index or iterating through them. Then I have the following problem.

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Answer 1

Type *Members does not support indexing, type Members does.

m := make([]Members, 5)
pm := &m

m[:2]     // good
pm[:2]    // bad
(*pm)[:2] // good

---

http://play.golang.org/p/_26TUBHdDm

package main

import "fmt"

type Member struct {
    Name, Surname string
    Age           int
}
type Members []Member

func main() {
    members1 := Members{
        {"Bob", "Doe", 30},
        {"Jack", "Doe", 30},
        {"John", "Doe", 30},
    }
    members1.ModifyName()
    members1.ModifyAllNames1()
    members1.ModifyAllNames2()
    fmt.Println(members1)
}

func (members *Members) ModifyName() {
    (*members)[0].Name = "-"
}

func (members *Members) ModifyAllNames1() {
    for i := 0; i < len(*members); i++ {
        (*members)[i].Name = "-"
    }
}

func (members *Members) ModifyAllNames2() {
    for _, m := range *members {
        m.Name = "-"
    }
}

Answer 2

func (members *Members) ModifyName() {
    *members[0].Name = "-"
}

invalid operation: members[0] (type *Members does not support indexing)

The issue is that of operator associativity and/or precedence, although I couldn't find this specific case explicitly covered within the Golang spec.

The expression *members[0].Name appears to be equivalent to *(members[0].Name), so, to get the proper pointer deference, you gotta use a pair of parentheses explicitly around the item that must be dereferenced, as is, (*members)[0].Name.