setzer22 / mutant-types

A library for creating clojure mutable types for when you really need it!

Mutant Types

This small clojure library allows you to define Mutables, a kind of deftype with all of its fields marked as :unsynchronized-mutable which allows setting values from outside and works like a regular map (i.e. Implements ILookup like defrecord).

As with regular deftype, type hints work, and primitive type hints internally create a Java class with primitive types. Similarly, other kinds of type hints are used by the compiler but will not be enforced at runtime (i.e. you can set a field hinted as ^Integer to the value "Hello", but not if it's an ^int).

The defmutable in this repo is inspired by the great https://github.com/arcadia-unity/Arcadia library.

Usage

Mutables follow the same structure as a deftype. Here's an example:

(require '[mutant.core :as mut])

(mut/defmutable MyType [^int a, ^String b])

(let [m (->MyType 1 "2")]
  (mut/mut! m :a 25)
  (mut/mut! m :b "Hello")
  (println (:a m)) ; => 25
  (println (:b m)) ; => "Hello"
  
  (mut/mut! m :a "Hello") ; => ClassCastException
  (mut/mut! m :b 3)); => This works

Note

Clojure doesn't have a macro like this for a good reason. Most of the time there is no need for the kind of Mutables introduced by this project. This should only be used in very tight loops of the codebase, and always as an implementation detail, never as part of an API.

Please use with caution and only when really necessary. Also remember to always measure first before optimizing!