/go-control-flow

Switch Patterns

Detailed patterns for Go switch statements, including expression-less switches, comma cases, break behavior, and labeled breaks.

No Automatic Fallthrough

Go switch cases do not fall through by default (unlike C/Java). Each case body implicitly breaks. Use fallthrough only when explicitly needed — it is rare in idiomatic Go.

switch n {
case 1:
    fmt.Println("one")
    // no fallthrough — next case is NOT executed
case 2:
    fmt.Println("two")
}

Expression-less Switch

A switch with no expression switches on true. Use it for clean if-else-if chains when comparing a single variable against multiple conditions:

func unhex(c byte) byte {
    switch {
    case '0' <= c && c <= '9':
        return c - '0'
    case 'a' <= c && c <= 'f':
        return c - 'a' + 10
    case 'A' <= c && c <= 'F':
        return c - 'A' + 10
    }
    return 0
}

Comma-Separated Cases

Multiple values can share a single case body using commas — no need for fallthrough:

func shouldEscape(c byte) bool {
    switch c {
    case ' ', '?', '&', '=', '#', '+', '%':
        return true
    }
    return false
}

Break with Labels

break inside a switch terminates only the switch, not an enclosing for loop. Use a label to break out of the loop:

Loop:
    for n := 0; n < len(src); n += size {
        switch {
        case src[n] < sizeOne:
            break        // breaks switch only
        case src[n] < sizeTwo:
            if n+1 >= len(src) {
                break Loop   // breaks out of for loop
            }
        }
    }

Another common pattern — breaking a range loop from inside a switch:

Loop:
    for _, v := range items {
        switch v.Type {
        case "done":
            break Loop  // breaks the for loop
        case "skip":
            break  // breaks only the switch
        }
    }

Rule of thumb: Whenever you have a switch inside a for and need to exit the loop from a case, always use a labeled break.

Type Switches

For type switches (switch v := x.(type)), see go-interfaces: Type Switch.

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