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cognitect / transit-cljs

Transit for ClojureScript
http://transit-format.org
Apache License 2.0
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Support for MapEntry writing #33

Closed rauhs closed 6 years ago

rauhs commented 7 years ago

New CLJS type MapEntry should be handled by the writer.

mfikes commented 6 years ago

See more details in #42 justifying this given transit-clj supports it, and its greater importance now, given the changes in ClojureScript master that emit cljs.core/MapEntry instances when seqs are formed over hash maps. Additionally #42 shows that the older cljs.core/BlackNode and cljs.core/RedNode should be supported as well.

mfikes commented 6 years ago

@swannodette Raised a good point in that this ticket could use a little more clarification. In particular, things can get messy if you are open to the idea the sorted map entries may not be terminal, thus raising the question of how exactly they should be encoded.

I took a look at the specs to ascertain what transit-clj was doing:

Any Clojure hash or sorted map entry me satisfies both 

(instance? clojure.lang.IPersistentVector me)

and

(instance? java.util.List me)

Thus, Clojure unambiguously maps map entry values to the Transit array semantic type.

What should ClojureScript do? The mapping table for ClojureScript indicates that cljs.core/IVector is mapped to the array semantic type when writing.

Any ClojureScrhipt hash or sorted map entry me satisfies

(satisfies? cljs.core/IVector me)

Thus it seems cut-an-dry that the ClojureScript map entries should be mapped to the array semantic type upon writing, not because cljs.core/IMapEntry has any specified mapping in the table, but because cljs.core/IVector does.

I'm tempted to simplify the above by saying that if a value v satisfies vector? in either Clojure or ClojureScript, then that value should be mapped to the array transit semantic type, but in reality the Clojure and ClojureScript language-level binding specifications are written in terms of Java interfaces and ClojureScript protocols, not in-language predicates like vector?.

swannodette commented 6 years ago

Fixed https://github.com/cognitect/transit-cljs/commit/a4d7dd3ea550b807597cf1908088d66d34c3d3d7