如何在for循环中组合多个赋值和Range

Question

I'm trying to figure out how to (or if it's possible to) combine multiple assignment and ranges in Golang

ex pseudo code of what I'd like to do

files := [2]*os.File{}

for i, _, fileName := 0, range os.Args[1:3] {
  files[i], _ = os.Open(fileName)
}

The idea being I want to have both an iteration counter (i) and the filenames (fileName). I know this can be achieved by using the key from range and some math (key -1), thats not the point of the example.

Edit:

Upon debugging the above example, I learned that i will range 0-1 in that example; Because os.Args[1:2] is a slice and that slice has indexing 0-1 . Therefore I dont need "some math" to properly index the keys.

** EDIT 2: ** This post is also a must read as to why the above [2]*os.File{} is not idiomatic go, instead it should not have a size specified (files := []*os.File{}) so that files is of type slice of *os.File

Answer 1

There are a lot of different issues here. First, range already does what you want. There's no need for even math.

for i, fileName := range os.Args[1:] {

i will range from 0 to 1 here, just like you want. Ranging over a slice always starts at index 0 (it's relative to the start of the slice). (http://play.golang.org/p/qlVM6Y7yPD)

Note that os.Args[1:2] is just one element. You probably meant it to be two.

In any case, this is likely what you really meant:

http://play.golang.org/p/G4yfkKrEe7

files := make([]*os.File, 0)

for _, fileName := range os.Args[1:] {
    f, err := os.Open(fileName)
    if err != nil {
        log.Fatalf("Could not open file: %v", err)
    }
    files = append(files, f)
}
fmt.Printf("%v
", files)

Fixed-length arrays are very uncommon in Go. Generally you want a slice, created with make.