strings: use a closure for FieldsFunc may result in a panic

go1.3.1

FieldsFunc runs over the runes twice. If a closure is used, and the underlying state
does't match the first run, there may be a panic.

The following panics (http://play.golang.org/p/P1MKh8GKaF)

    state := false
    f := func(c rune) bool {
        switch c {
        case '1':
            fmt.Println(state)
            state = !state
            return state
        default:
            fmt.Println("true")
            return true
        }
    }
    strings.FieldsFunc(" 1", f)




This should be safe from panics, or at least clearly document that FieldsFunc is run
twice.

Comment 1:

I think we should document the behaviour.

Labels changed: added repo-main, release-go1.4, documentation.

Comment 2:

CL https://golang.org/cl/143260045 mentions this issue.

Comment 3:

This issue was closed by revision e9ec8e7.

Status changed to Fixed.

bytes, strings: document that FieldsFunc f must not be stateful

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strings: use a closure for FieldsFunc may result in a panic #8738

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strings: use a closure for FieldsFunc may result in a panic #8738

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ianlancetaylor commented on Sep 15, 2014

gopherbot commented on Sep 18, 2014

rsc commented on Sep 18, 2014

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