Stringer in Go

A String method changes how fmt prints your type.

type Stars int

func (s Stars) String() string {
    if s < 0 || s > 3 {
        return "invalid"
    }
    return strings.Repeat("*", int(s)) + strings.Repeat(".", 3-int(s))
}

type Step struct {
    Title string
    Stars Stars
}

func (s Step) String() string {
    return fmt.Sprintf("%-12s %s", s.Title, s.Stars)
}

func show() string {
    return fmt.Sprint(Step{Title: "Slices", Stars: 2})
}

How it works

1. fmt.Stringer is the one-method interface fmt looks for.
2. Use a value receiver, or printing a value will not find it.
3. Never call fmt.Sprintf(\u0022%v\u0022, x) inside x.String().

Keywords and builtins used here

• func
• if
• int
• return
• string
• struct
• type

The run, in numbers

Lines

21

Characters to type

362

Tokens

110

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 63 seconds.

Type this snippet

Step 2 of 3 in Standard interfaces, step 11 of 19 in Interfaces & generics.

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