What\'s the Difference Between a Type Declaration and Inheritance in Go\'s `PublicKey` Example?

Demystifying Type Declarations: The Curious Case of PublicKey

In the realm of Go programming, one may encounter a peculiar type declaration syntax like:

// PublicKey is the type of Ed25519 public keys.
type PublicKey []byte

This declaration raises questions: Does it create a new struct inheriting from []byte? Is it merely an alias? And isn't inheritance forbidden in Go?

The answer lies in the concept of type declaration, specifically type definition. It creates a new type, named PublicKey, with []byte as its underlying type. This type now has a distinct identity from its underlying type.

Type Definitions:

Type definitions serve several purposes:

• Convenience: Using a custom type instead of its underlying type makes code more readable and maintainable.
• Expressiveness: Custom type names can convey the intended purpose or structure of data.
• Extensibility: Custom types can be extended with methods, unlike built-in types.

Methods and Interfaces:

Only types with methods can implement interfaces. Interfaces define a set of methods that a type must implement. By creating new types, it becomes possible to define methods that align with the requirements of specific interfaces.

For example, []int cannot implement sort.Interface (required for sorting), so a new type sort.IntSlice is created to attach the required methods. This allows you to sort values of type sort.IntSlice but not []int.

Embeddings and Inheritance:

Contrary to inheritance, embedding allows one type to include the fields and methods of another type. However, the embedded type does not inherit the methods of the embedding type.

In conclusion, type declarations in Go enable the creation of new, convenient, and extensible types. They allow you to attach methods and implement interfaces, thus extending the capabilities of existing types without resorting to inheritance.

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