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Add sealed module: modelling domains with sealed types and exhaustive switch

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Payment model, permits and the three modifiers, default-branch trap, generic and recursive hierarchies, visitor comparison, run-time enforcement, modules. Transcripts from JDK 21, 25 and 27.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01TF9JWFvJSNm6HVzswzZU5a
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Claude
2026-09-24 12:03:59 +00:00
parent 65a4bbbbe3
commit ff6130bede
38 changed files with 638 additions and 0 deletions
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sealed/broken/VisitorAdded.java
+17
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public class VisitorAdded {
interface Payment { <R> R accept(Visitor<R> v); }
interface Visitor<R> { R visitCard(Card c); R visitUpi(Upi u); R visitWallet(Wallet w); } // Wallet added here
record Card() implements Payment { public <R> R accept(Visitor<R> v) { return v.visitCard(this); } }
record Upi() implements Payment { public <R> R accept(Visitor<R> v) { return v.visitUpi(this); } }
record Wallet() implements Payment { public <R> R accept(Visitor<R> v) { return v.visitWallet(this); } }
// Two existing operations, neither knows about Wallet: each one now fails to compile.
static class Fee implements Visitor<Long> {
public Long visitCard(Card c) { return 2L; }
public Long visitUpi(Upi u) { return 0L; }
}
static class Label implements Visitor<String> {
public String visitCard(Card c) { return "card"; }
public String visitUpi(Upi u) { return "upi"; }
}
}