Interfaces are satisfied implicitly in Go

No implements keyword: a type has the methods, so it fits.

type Scorer interface {
    Score() int
}

type Snippet struct{ Lines int }
type Script struct{ Lines int }

func (s Snippet) Score() int { return s.Lines }
func (s Script) Score() int  { return s.Lines * 2 }

var _ Scorer = Snippet{} // fails to compile if the method is missing

func total(items []Scorer) int {
    sum := 0
    for _, item := range items {
        sum += item.Score()
    }
    return sum
}

How it works

The interface can be declared after the types that satisfy it.
Small interfaces are the Go habit — often one method.
A compile-time assertion documents the intent.

Keywords and builtins used here

for
func
int
interface
range
return
struct
type
var

The run, in numbers

Lines: 19
Characters to type: 382
Tokens: 95
Three-star pace: 100 tpm

At the three-star pace of 100 tokens a minute, this run takes about 57 seconds.

Type this snippet

Step 2 of 4 in Interfaces, step 5 of 19 in Interfaces & generics.

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