How does struct embedding promote methods in Go, and how does it differ from inheritance?

Go uses composition through embedding rather than class inheritance. When a type is embedded (without a field name), its exported methods and fields are promoted to the outer type — they are directly accessible. However, the outer type is NOT a subtype of the embedded type.

type Logger struct{ prefix string }

func (l *Logger) Log(msg string) {
    fmt.Printf("[%s] %s\n", l.prefix, msg)
}

// Server embeds Logger — gains the Log method
type Server struct {
    *Logger               // embedded pointer (promotes Log)
    host string
    port int
}

srv := Server{
    Logger: &Logger{prefix: "SERVER"},
    host: "localhost",
    port: 8080,
}
srv.Log("starting")        // SERVER: starting — promoted method!
srv.Logger.Log("starting") // same thing, explicit call

// Method override — Server can define its own Log
func (s *Server) Log(msg string) {
    s.Logger.Log(fmt.Sprintf("%s:%d — %s", s.host, s.port, msg))
}

// KEY: embedding is NOT inheritance
type Describer interface{ Describe() string }
type Base struct{}
func (Base) Describe() string { return "I am Base" }

type Derived struct{ Base }
// Derived satisfies Describer via promotion:
var d Describer = Derived{}  // works!

// BUT: you CANNOT use Derived where Base is required
func process(b Base) {}
// process(Derived{})  // COMPILE ERROR — not a subtype!

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