Introduction to the Java Optics

Functional Optics for Modern Java series

Part 1. The Immutability Gap: Why Java Records Need Optics

Part 2. Optics: Lenses, Prisms, and Traversals in Practice

Useful links:

JEP 468. Derived Record Creation

Runnable Demos on GitHub.

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Optics Fundamentals

• Lenses
• Prisms
• Affines
• Isomorphisms
• Composition rules

                    ┌─────────┐
                    │  Fold   │  (read-only, zero-or-more)
                    └────┬────┘
                         │
              ┌──────────┴──────────┐
              │                     │
         ┌────┴────┐          ┌─────┴─────┐
         │ Getter  │          │ Traversal │  (read-write, zero-or-more)
         └────┬────┘          └─────┬─────┘
              │                     │
              │               ┌─────┴─────┐
              │               │           │
         ┌────┴────┐    ┌─────┴─────┐ ┌───┴───┐
         │  Lens   │    │  Affine   │ │Setter │
         └────┬────┘    └─────┬─────┘ └───────┘
              │         (zero-or-one)
              │               │
              │         ┌─────┴─────┐
              │         │   Prism   │
              │         └─────┬─────┘
              │               │
              └───────┬───────┘
                 ┌────┴────┐
                 │   Iso   │  (exactly-one, reversible)
                 └─────────┘

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Further reading: Higher-Kinded-J. Composable Effects and Advanced Optics for Java