你如何从clojure的瞬态地图中获取密钥？

Question

I am trying to get the seq of all of the keys in a transient map:

(keys {3 4 5 6 7 8}) gives (3 5 7)

as I expect but:

(keys (transient {3 4 5 6 7 8}))

gives

#<CompilerException java.lang.IllegalArgumentException: Don't know how to create ISeq from: clojure.lang.PersistentArrayMap$TransientArrayMap (NO_SOURCE_FILE:346)>

on the same note, how do I process using a transient map?

(map identity {3 4 5 6})

gives

([3 4] [5 6])

but

(map identity (transient {3 4 5 6}))

gives

#<IllegalArgumentException java.lang.IllegalArgumentException: Don't know how to create ISeq from: clojure.lang.PersistentArrayMap$TransientArrayMap>

Answer 1

This isn't really possible because of the interaction between laziness and mutability. (keys m) always returns a lazy sequence backed by the immutable m data structure, computing elements as necessary. But if m is a transient, it might change at any time, which would ruin the lazy key-sequence. You're really meant to not do anything too fancy with transients; and because it's so cheap to create transient or persistent versions of a data structure, it's not too onerous to go back and forth a few times if you really want to do something fancy.

Answer 2

I don't think there's a way to work on transients like you work on persistent structures. You need to create a persistent structure from your transients with persistence!

user> (map identity (persistent! (transient {3 4 5 6})))
([3 4] [5 6])

You can learn more about transients from Clojure docs .