copying: deep vs shallow copy module (clone() traps, copy constructors, serialization copy, records, defensive copies, collection copies), 17 contract tests

Co-Authored-By: Claude Sonnet 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_017ic4b4X2xx7RrveVQU9R1N
2026-11-12 20:18:06 +05:30
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+== 1. A record does not copy the list you give it ==
+  leaky.items()         = [pen, book, laptop]
+  after leaky.items().add("phone"), basket = [pen, book, laptop, phone]
+
+== 2. List.copyOf in the compact constructor ==
+  safe.items()          = [pen, book]
+  safe.items().add(...) -> UnsupportedOperationException
+
+== 3. 'Changing' a record means building a new one ==
+  safe   = SafeOrder[id=A-2, items=[pen, book]]
+  bigger = SafeOrder[id=A-2, items=[pen, book, charger]]
+
+== 4. A mutable Date component ==
+  LeakyEvent.when().getTime() after caller mutates d1 = 86400000
+  SafeEvent.when().getTime()  after both mutations    = 0