Add CodingKeyRepresentable support for dictionary keys instead of LosslessStringConvertible
#216
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…LosslessStringConvertible` Fixes #99
sindresorhus
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hank121314
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Oct 3, 2025
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Fixes #99
I don't expect to merge this anytime soon because of the system requirements and it being a breaking change, but I would like a review.
Why CodingKeyRepresentable instead of LosslessStringConvertible?
CodingKeyRepresentable is the better choice because:
Designed for dictionary keys: CodingKeyRepresentable was specifically created to enable
non-String/Int types as Codable dictionary keys. It's purpose-built for this exact use case.
Better enum support: Enums with Int raw values get automatic CodingKeyRepresentable conformance from the standard library.
Cannot support both: Swift explicitly forbids multiple conditional conformances of Dictionary to Serializable, even with different conditional bounds. We must choose one approach.
What works as dictionary keys?
Types that are only LosslessStringConvertible (like Bool) won't work. However, these are uncommon as dictionary keys and using them often indicates a design issue.