From e7df71bbbdadbd11b7c55b82fc468f9550b5b027 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Tue, 28 Jul 2026 21:26:42 +0100
Subject: Generate hashCode directly

---
 .../javatransient0/JavaTransient0Generator.java    | 63 ++++++++++++++--------
 1 file changed, 40 insertions(+), 23 deletions(-)

diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatransient0/JavaTransient0Generator.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatransient0/JavaTransient0Generator.java
index 1e2c07c..edfc354 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatransient0/JavaTransient0Generator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatransient0/JavaTransient0Generator.java
@@ -117,29 +117,18 @@ public class JavaTransient0Generator implements Generator {
                             ))
                         )))
                     ),
-                    new JavaMethodDeclaration(
-                        JavaIdentifier.of("hashCode"),
-                        JavaVisibility.PUBLIC,
-                        JavaMemberKind.INSTANCE,
-                        JavaTypeRef.INT,
-                        List.of(),
-                        List.of(),
-                        Optional.of(new JavaBlock(List.of(
-                            // TODO: implement directly
-                            new JavaReturn(new JavaStaticMethodCall(
-                                JavaTypeRef.OBJECTS,
-                                JavaIdentifier.of("hash"),
-                                List.of(
-                                    new JavaFieldAccess(JavaRef.THIS, typeId),
-                                    new JavaStaticMethodCall(
-                                        JavaTypeRef.SYSTEM,
-                                        JavaIdentifier.of("identityHashCode"),
-                                        List.of(new JavaFieldAccess(JavaRef.THIS, value))
-                                    )
-                                )
-                            ))
-                        )))
-                    )
+                    generateHashCode(List.of(
+                        new JavaStaticMethodCall(
+                            JavaTypeRef.LONG_BOXED,
+                            JavaIdentifier.of("hashCode"),
+                            List.of(new JavaFieldAccess(JavaRef.THIS, typeId))
+                        ),
+                        new JavaStaticMethodCall(
+                            JavaTypeRef.SYSTEM,
+                            JavaIdentifier.of("identityHashCode"),
+                            List.of(new JavaFieldAccess(JavaRef.THIS, value))
+                        )
+                    ))
                 ),
                 DocComment.EMPTY
             ))
@@ -1142,6 +1131,34 @@ public class JavaTransient0Generator implements Generator {
         return this.javaGenerator.generateFieldName("decode" + type.name());
     }
 
+    private JavaMethodDeclaration generateHashCode(List<JavaExpression> fieldHashCodes) {
+        JavaExpression hashCodeExpression = new JavaIntegerLiteral(17);
+
+        for (var fieldHashCode : fieldHashCodes) {
+            hashCodeExpression = new JavaBinaryOperation(
+                JavaBinaryOperator.ADD,
+                new JavaBinaryOperation(
+                    JavaBinaryOperator.MULTIPLY,
+                    new JavaIntegerLiteral(37),
+                    hashCodeExpression
+                ),
+                fieldHashCode
+            );
+        }
+
+        return new JavaMethodDeclaration(
+            JavaIdentifier.of("hashCode"),
+            JavaVisibility.PUBLIC,
+            JavaMemberKind.INSTANCE,
+            JavaTypeRef.INT,
+            List.of(),
+            List.of(),
+            Optional.of(new JavaBlock(List.of(
+                new JavaReturn(hashCodeExpression)
+            )))
+        );
+    }
+
     private static class Context {
         private final TypesInfo typesInfo;
 
-- 
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