Clojure 1.13.0-alpha8

Clojure 1.13.0-alpha8 is now available! Find download and usage information on the Downloads page.

Selectors

A developer may need to apply the same key-selection logic embedded in a map destructuring form (as directives, :keys!/:syms!/:strs!/etc., nesting, etc.) against multiple maps, or want to hand that selection logic to another part of the program. Currently that logic is oriented around binding in destructuring and not for programmatic use.

This release adds a new selector macro that takes a destructuring form and returns a function that can be applied to maps:

(selector [m])

  Builds a selecting-fn from m, a map destructuring form that must
  include one or more of the :select, :all, :missing, and :excess
  directives. The return function takes a collection, destructures it
  per m, and returns a map of the result(s).

  If m has exactly one directive, the result is the value that
  directive would yield. If m has more than one directive, then it
  returns a map of directives to values.

  As in destructuring, :missing controls whether missing required keys
  throw or are collected.

  While a map destructuring form may and sometimes must include
  bindings, selector doesn't produce bindings, thus ignoring the
  associated directive names.

  Throws an exception if the argument is not a map.

• CLJ-2979 selector

Transient map performance

This release contains many performance improvements around the use of maps, particularly transient maps, and functions like into, merge, and merge-with.

Transient array maps now grow larger before transitioning to transient hash maps (similar to recent persistent array map changes), and can be loaded significantly faster. The increased use of persistent and transient array maps will also make many more call sites inside the Clojure runtime monomorphic, encouraging greater JVM inlining. For more info see CLJ-2980.

Improvements and bug fixes

• CLJ-2939 QualifiedMethodExpr field overload does not propagate field type - fixed
• CLJ-1468 merge-deep, merge-deep-with - added recursive merge fns
• CLJ-2981 merge - added tests
• CLJ-2623 tagged literals and Java constructors - allow full unicode for first char
• CLJ-2623 tagged-literal equality - check tag before form for performance
• CLJ-2842 defn - does not needlessly initialize class when defn returns class
• CLJ-2896 clojure.zip/next - only call zip/up once (not 3x)
• CLJ-2915 ExceptionInfo - added to default imports, so no import or qualification needed

Try it out

Update your deps.edn :deps with:

org.clojure/clojure {:mvn/version "1.13.0-alpha8"}

Start a REPL with the Clojure CLI (any version) with:

clj -Sdeps '{:deps {org.clojure/clojure {:mvn/version "1.13.0-alpha8"}}}