This should be polymorphic. Alternatives:

1) Use JSON encoder

• most likely does the job already.
• requires dependency to JSON library
• compojure-api does this

2) Multimethod

• e.g. reitit.core/stringify
• Easy to implement
• Value-based, works for all coercion instances
• Slow(er than Protocol)
• Adding new types (e.g. LocalTime) requires imperative registration.
  • Extending just for routing, can't (shoudn't) use it elsewhere

3) Protocol

• e.g. reitit.core/Stringify
• Easy to implement
• Value-based, works for all coercion instances
• Fast(er than Multimethod)
• Adding new types (e.g. LocalTime) is more declarative
  • Extending just for routing, can't (shoudn't) use it elsewhere
• bidi does this

4) Coercion/Type-based

• bijections, defined for all types of coercion
• both coercion & uncoercion defined in the type meta data
• works for all use cases, not just routing (where else this is really needed?)
• parameter type needs to be defined in order to work
• e.g. with spec tools to keyword?:

(st/spec
  {:spec keyword?
   :description "a bijecting keyword"
   ::encode/string #(name %2)
   ::decode/string #(keyword %2)})

NOTE: qualified keywords as path-parameters need to be url-encoded, as otherwise the / with mess up the generated path. We still could use the generic ::encode/string, just url-encode the results.

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From my point of view, 3rd option (Protocol) is the more natural choice here, since I don't see any other usage of this except for the routing

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I think it's the way to go. When/if 4rd is implemented, it can be used instead. Would you like to do a PR?

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I have extra time just now, will do this.

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#76

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fixed in [metosin/reitit-core "0.1.1-20180322.170157-5"].

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