(deftype) blues - private and mutable field access problems

Mon, 20 May 2024 18:15:40 +0000

New to clojure, trying to define an effective class with mutable fields via deftype, definitions below.

My program is single threaded, no one else will ever use my code, promised. I know all the advantages of immutability, but this program makes over 500,000,000 updates, so the GC would be the main actor, not my code. I've tried that.

Two problems I've got at run time.

*1. ; Execution error (IllegalArgumentException) at layout.core.Individual/idivlCopy (core.clj:161).
    ; No matching field found: fitness for class layout.core.Individual

I understand that the fields of a deftype are not public, but the code of idivlCopy is in the deftype itself. It seems to me, that the runtime knows (.fitness this) but not (.fitness that).

What is the rationale of this behaviour and how can I get around it?
How can I access the private protected fields (of that) from the private (i.e. deftype) code area?!

*2. ; Execution error (ClassCastException) at layout.core.Individual/idivlSwap (core.clj:173).
           ; class clojure.core.Vec cannot be cast to class clojure.lang.IEditableCollection
           ;    (clojure.core.Vec and clojure.lang.IEditableCollection are in unnamed module of loader 'app')

The annotations tell that both fields are volatile-mutable. Why is this not known at run time for the chromosome vector? Why can't I (assoc! ) my volatile-mutable chromosome vector-of :char -s?

(definterface IIndividual

  (idivlCopy [that])                      ; Copies that Individual to this
  (idivlSwap [^Integer xP, ^Integer xQ])) ; Swaps two genes in the chromosome
  ; and somme more.
)

(deftype Individual                ; An individual has a fitness value and a chromosome
  [^{:volatile-mutable true}  ^Integer fitness,       ; Integer
   ^{:volatile-mutable true}           chromosome]    ; vector-of :char
 
  IIndividual

	:
	.

  (idivlCopy         ; Copies that Individual to this
    [_, that] 
*1  (set! fitness    (.fitness    that))         ; (set! fitness  999) worked!!
    (set! chromosome (.chromosome that))
    nil)

  (idivlSwap         ; Swaps the genes in the chromosome at alleles P and Q
    [this,
     ^Integer iP,                 ; index of allele P
     ^Integer iQ]                 ; index of allele Q
    (let [gP (chromosome iP),     ; gene  at allele P
          gQ (chromosome iQ)]     ; gene  at allele Q
*2    (assoc! chromosome iP gQ)
      (assoc! chromosome iQ gP)
      nil))

    ; and some more
    :
	.
)

volatile-mutable not recognized in some deftype method subforms

Wed, 21 Dec 2022 17:46:19 +0000

This is a somewhat contrived example but there is a curious behavior that may or may not be a bug.

Suppose you have the following protocol:

(defprotocol P (f [this]))

And concrete type with a mutable parameter and lock:

(deftype T [^:volatile-mutable x lock]
  P
  (f [this]
    (locking lock
       (set! x true)
       (prn ""))))

Compiler has no problem with this. But move the (prn "") statement outside the (locking …) block and you get:

(deftype T [^:volatile-mutable x lock]
  P
  (f [this]
    (locking lock
      (set! x true))
    (prn "")))

Syntax error (IllegalArgumentException) compiling fn* at (REPL:4:5).
Cannot assign to non-mutable: x

David Miller spotted this behavior in the lastest ClojureCLR (see https://clojure.atlassian.net/browse/CLJCLR-122) and is sleuthing it on his end but the fact the same error is raised in JVM Clojure suggests that either there is a bug in Clojure proper, or some highly counterintuitive rule is at work here, the details of which are probably worth understanding. Why the compiler would view x as non-mutable here is not clear.

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(deftype) blues - private and mutable field access problems

volatile-mutable not recognized in some deftype method subforms