Type switches in Go

One switch over the dynamic type inside an interface value.

func describe(value any) string {
    switch typed := value.(type) {
    case nil:
        return "nothing"
    case int:
        return fmt.Sprintf("int %d", typed*2)
    case string:
        return "string " + strings.ToUpper(typed)
    case []int:
        return fmt.Sprintf("%d ints", len(typed))
    case error:
        return "error " + typed.Error()
    default:
        return fmt.Sprintf("something else: %T", typed)
    }
}

How it works

1. switch v := x.(type) binds v with the case's type.
2. A nil case catches an interface holding nothing.
3. The default arm is what keeps it honest.

Keywords and builtins used here

• any
• case
• default
• error
• func
• int
• len
• return
• string
• switch
• type

The run, in numbers

Lines

16

Characters to type

353

Tokens

89

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 51 seconds.

Type this snippet

Step 1 of 2 in Dynamic types, step 8 of 19 in Interfaces & generics.

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