隐含索引时，Golang中“ for…range”的迭代顺序

Question

https://golang.org/ref/spec#For_range

For statements with range clause

For an array, pointer to array, or slice value a, the index iteration values are produced in increasing order, starting at element index 0. If at most one iteration variable is present, the range loop produces iteration values from 0 up to len(a)-1 and does not index into the array or slice itself. For a nil slice, the number of iterations is 0.

According to the spec, iterating over a linear data structure (array or slice or string) in Go will get each of elements in there always in order the index increases.

for i, v := range []int{11, 22, 33, 44} {
    fmt.Println(i, v)
}

But the thing is that I can't really find in the spec the guarantee that,

this range-iterate-over clause with an implicit index iteration value, too, will always keep the same order as well:

for _, v := range []int{11, 22, 33, 44} {
    fmt.Println(v)
}

Will those two examples I put above always perform in the same order?

I assume they do but I haven't heard the promise yet.

How does for ... range work when the index iteration value is represented by the blank identifier(the underscore _)?

Answer 1

It's in the spec, but I think you overlook something. There are iteration values and iteration variables.

For each entry it assigns iteration values to corresponding iteration variables if present and then executes the block.

And your quote refers to iteration values:

For an array, pointer to array, or slice value a, the index iteration values are produced in increasing order, starting at element index 0. If at most one iteration variable is present, the range loop produces iteration values from 0 up to len(a)-1 and does not index into the array or slice itself.

So as you can see, regardless of how many iteration variables there are, the iteration values are always in increasing order, starting at element index 0.

And the second iteration value is always a[i], where i corresponds to the first iteration value, the index:

Range expression                          1st value          2nd value

array or slice  a  [n]E, *[n]E, or []E    index    i  int    a[i]       E