This code is illegal in Go

    item := item
    item := item

"no new variables on left side of :="

You can't declare the same variable twice in the same scope.

    item := item

works only because it declares a new variable in the current scope, initialized with a variable with the same name (but different variable) from the outer scope.

Go distinguishes declarations from assignments. In this example, the second assignment is a no-op indeed.

    item := item
    item = item