Immutability

Kind: principle

Layer: Computation Core

Record: architecture:immutability

Severity: recommended

Scope: data, value object, concurrency

Canonical: Ontology

A design rule that a value is never changed after it is created, and a change produces a new value.

Listed in Architecture principles, after Pure Functions and before Reproducibility.

Requires

• Value Semantics

Reinforces

• Thread Safety
• Predictability

Enables

• Safe Sharing

Conflicts with

• Shared Mutable State

In tension with

• Allocation Cost

Tensions

• Immutability / Allocation Cost

Violated by

• Shared Mutable State
• Exposed Internals

Refactored by

• Make Immutable

Severity

• recommended

Category

• Correctness / Determinism / Verification

Reinforced by

• Value Object
• Independent Lifetime Axes

Required by

• Referential Transparency

Linked from

• The board and the venue
• Stating an invariant
• Computation and resource
• Separate, trade, or mitigate
• The principle architecture
• Anti-patterns
• Domain Architecture
• Correctness / Determinism / Verification
• Core Modular Design
• Coordination Surfaces
• Core Modular Design
• Correctness / Determinism / Verification
• Transactions / State / Concurrency
• Severity levels
• The resolutions