What is protocol composition? How does it relate to Codable?

Sources & Resources

Main Source: 🔗 Ace the iOS Interview

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TL/DR

The Codable protocol is a prime example of Swift’sprotocol composition feature which allows you to easily combine existing protocols together using the & operator.

For example, the Codable protocol is actually thecombination of the Encodable and Decodable protocols.

typealias Codable = Decodable & Encodable

Decodable allows a type to decode itself from an external representation and Encodable allows a type to encode itself as an external representation.

When combined together like this, the Codable protocol ensures that whatever object implements this protocol can both convert and be converted from some externalrepresentation.

In practice, this typically means converting a JSON response to a domain model object and vice-versa.