Why Doesn’t JSONEncoder Conform to the Encoder Protocol?
Inspecting the source code for
JSONEncoder, we see it’s aopentype that internally uses aprivatetype_JSONEncoder, which does conform toEncoder.[…]
But why were they designed that way? Why not just make
JSONEncoderanEncodertoo?In short, the answer is that they provide very different APIs. The
JSONEncoderAPI is designed to provide a single, simple entry point into encoding, and theEncoderprotocol provides a completely different API for customizing how types are encoded.
This makes sense, though it’s kind of odd that the facade and the protocol for the private types both use the same word (Encoder/Decoder). Cocoa distinguishes between NSArchiver/NSUnarchiver, which you use directly, and NSCoder, which is passed to you. Although, that’s also a bit messy because the archivers are subclasses of NSCoder, and so all the other methods are still there.
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When implementing a SQLite encoder/decoder (https://shareup.app/blog/encoding-and-decoding-sqlite-in-swift/), I too was initially confused by the labyrinth of similarly-named types, but it turned out to be a pretty elegant and flexible design, albeit one that requires a fair amount of boilerplate code.
