Created
November 7, 2022 17:44
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Simple mutable data class with clojure.asm
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| *clojure-version* ;; => {:major 1, :minor 10, :incremental 3, :qualifier nil} | |
| (System/getProperty "java.version") ;; => "14.0.1" | |
| (import [clojure.asm ClassVisitor ClassWriter Opcodes Type] | |
| [clojure.lang DynamicClassLoader RT]) | |
| (defn type-to-desc [t] | |
| (case t | |
| :int "I" | |
| ;; ... and so on | |
| (-> (Type/getType t) .getDescriptor))) | |
| (defn mutable-acc-type [class-name types] | |
| (let [base-type "java/lang/Object" | |
| cv (doto (ClassWriter. ClassWriter/COMPUTE_FRAMES) | |
| (.visit Opcodes/V1_7 | |
| (bit-or Opcodes/ACC_PUBLIC Opcodes/ACC_FINAL) | |
| (.replace class-name \. \/) | |
| nil base-type nil))] | |
| (doto (.visitMethod cv Opcodes/ACC_PUBLIC "<init>" "()V" nil nil) | |
| (.visitCode) | |
| (.visitVarInsn Opcodes/ALOAD 0) | |
| (.visitMethodInsn Opcodes/INVOKESPECIAL base-type "<init>" "()V" false) | |
| (.visitInsn Opcodes/RETURN) | |
| (.visitMaxs -1 -1) | |
| (.visitEnd)) | |
| (dorun (for [[i t] (map vector (range) types)] | |
| (doto (.visitField cv Opcodes/ACC_PUBLIC (str "m" i) (type-to-desc t) nil nil) | |
| (.visitEnd)))) | |
| (-> (RT/makeClassLoader) | |
| (.defineClass class-name (.toByteArray cv) nil) | |
| (.newInstance)))) | |
| (comment | |
| (def obj (mutable-acc-type "my.pkg.Foo" [:int Object String])) | |
| [(.m0 obj) (.m1 obj) (.m2 obj)] ;; => [0 nil nil] | |
| (do (set! (.m0 obj) 42) | |
| (set! (.m1 obj) [1 2 3]) | |
| (set! (.m2 obj) "fred")) | |
| [(.m0 obj) (.m1 obj) (.m2 obj)] ;; => [42 [1 2 3] "fred"] | |
| ) |
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