Reverse routing params conforming

[malchmih]

I'd be useful to have coercion to work with reitit/match-by-name. One example is conforming keyword to a string path parameter.
Related spec-tools issue: metosin/spec-tools#112

(r/match-by-name
  (r/router
    ["/olipa/:kerran" ::avaruus])
  ::avaruus
  {:kerran :joskus})
;#Match{:template "/olipa/:kerran",
;       :data {:name :user/avaruus},
;       :result nil,
;       :path-params {:kerran :joskus},   <-- wrong
;       :path "/olipa/:joskus"}           <-- wrong

[ikitommi]

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.

[malchmih]

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

[ikitommi]

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?

[ikitommi]

I have extra time just now, will do this.

[ikitommi]

#76

[ikitommi]

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