Updated: 2017-06-07 21:54:52 CST +08

Golang Delete Slice Item in Range Problem

Problem

When range start, it is not iterate value one by one, it is iterate by index.

If you modified a slice while it is in range, it will induce some problem.

Example

Remove char a from chars.

  • Incorrect Way

    chars := []string{"a", "a", "b"}
    
    for i, v := range chars {
        fmt.Printf("%+v, %d, %s\n", chars, i, v)
        if v == "a" {
            chars = append(chars[:i], chars[i+1:]...)
        }
    }
    fmt.Printf("%+v", chars)
    
    
    • Expected
    [a a b], 0, a
    [a b], 0, a
    [b], 0, b
    Result: [b]
    
    • Actual
    // Autual
    [a a b], 0, a
    [a b], 1, b
    [a b], 2, b
    Result: [a b]
    

    Playground

  • Correct Way

    chars := []string{"a", "a", "b"}
    
    for i := 0; i < len(chars); i++ {
        if chars[i] == "a" {
            chars = append(chars[:i], chars[i+1:]...)
            i-- // form the remove item index to start iterate next item
        }
    }
    
    fmt.Printf("%+v", chars)
    

    Playground