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bookComposition over Inheritance

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Composition Over Inheritance

Go uses composition rather than classical inheritance to share functionality between types. Instead of creating hierarchies with parent and child classes, you embed one struct inside another. This is called struct embedding.

With struct embedding, you place one struct as a field in another struct—without a field name. The outer struct automatically gains access to the methods of the embedded struct, as if they were its own. This provides code reuse, but avoids the tight coupling and complexity of inheritance chains found in other languages.

This approach promotes flexible design. You can mix and match behaviors by embedding different structs, creating types with only the features you need. There is no "is-a" relationship—composition models "has-a" or "can-do" relationships, making your codebase easier to maintain and extend.

main.go

main.go

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package main

import (
	"fmt"
)

// Logger provides logging functionality.
type Logger struct{}

func (l Logger) Log(message string) {
	fmt.Println("LOG:", message)
}

// User embeds Logger to gain logging ability without inheritance.
type User struct {
	Name   string
	Logger // Embedded struct
}

func main() {
	user := User{Name: "Alice"}
	user.Log("User created: " + user.Name)
}
question mark

Which statement best describes the benefit of struct embedding in Go compared to traditional inheritance?

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すべて明確でしたか？

どのように改善できますか？

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