Multi-variable short redeclaration when inside a for loop creates a new variable?

Question

The documenation states:

As a consequence, redeclaration can only appear in a multi-variable short declaration. Redeclaration does not introduce a new variable; it just assigns a new value to the original.

But how does this work in for loops? See this example. It seems that the variable "nextPos", which has a scope outside the loop, actually gets redeclared inside the loop for the inner scope, and thus looses its value for each iteration. This version works though.

Answer 1

Let's show how it works, with these code samples:

Let's simplify your first sample, see this working sample code (1):

package main

import "fmt"

func main() {
    a := 100
    {
        fmt.Println(a) // 100
        a, b := 0, 0
        fmt.Println(a, b) // 0 0
    }
    fmt.Println(a) // 100
}

output:

100
0 0
100

so a in a, b := 0, 0 is shadowed, this a is new variable,
this is called Variable scoping and shadowing,
and you may name it e.g. c like this code for now to show how it works (2):

package main

import "fmt"

func main() {
    a := 100
    {
        fmt.Println(a) // 100
        c, b := 0, 0
        fmt.Println(c, b) // 0 0
    }
    fmt.Println(a) // 100
}

the output is that same as (1):

100
0 0
100

and lets simplify your next sample code (3):

package main

import "fmt"

func main() {
    a := 0
    b := byte(0)
    {
        fmt.Println(a, b) // 0 0
        a, b = 1, byte(1)
        fmt.Println(a, b) // 1 1
    }
    fmt.Println(a, b) // 1 1
}

output:

0 0
1 1
1 1

so here a and b are the same inside and outside loop.

also see: Where can we use Variable Scoping and Shadowing in Go?
and see: What is the difference between := and = in Go?