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This question is relate to this and this answer

All of these question & answer all make sense to me except one little thing.

If the 2nd value of for loop is a[i], then what is the different between the a[i] from the for loop and the a[i] as we write? It looks like the same thing but it isn't, right?

Please help me clear this out. Thanks guys!

Tiến Nguyễn Hoàng
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    If you use the value from range it is a copy at a different memory location. If you use a[idx] you are editing the memory in the slice. – Thomas Jun 05 '18 at 02:09

1 Answers1

3

When you write:

a := make([]int, 3)

a[0], a[1], a[2] = 1, 2, 3

for i, val := range a {
    println(a[i], "vs.", val)
    println(&a[i], "vs.", &val)
}

The variable val is assigned a copy of the value in a[i].

It is basically the same as doing it like this:

var val int
for i := range a {
    val = a[i]
    println(a[i], "vs.", val)
    println(&a[i], "vs.", &val)
}

So depending on what you are doing then:

It looks like the same thing but it isn't, right?

If you use the variable to read the value, then it is the same thing.

But if you assign to it, take it's pointer value, etc, it is not.

eugenioy
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