Go - "range variable i captured by func literal"

[huygn]

When doing anonymous function inside a for loop, you might see a warning range variable i captured by func literal.

for i, e := range itemIDs {
    // This work as expected
    ii, ee := i, e
    go func() {
        defer wg.Done()
        if err := GetStoryByID(ee, &items[ii]); err != nil {
            log.Fatalf("Error: %s", err)
        }
    }()

    // This WONT work as expected
    go func() {
        defer wg.Done()
        if err := GetStoryByID(e, &items[i]); err != nil {
            log.Fatalf("Error: %s", err)
        }
    }()
}

With our go func().. statement we start a new goroutine. They run concurrently, which they do not run one after the other in an orderly fashion. They could in theory run one after the other, or they could all run at the same time (in parallel). Or maybe the "last one" runs first and then the "first one" and the "second one" runs last, or maybe.. think you get the point; it's unpredictable.

Ref: http://oyvindsk.com/writing/common-golang-mistakes-1