Hidden Side Effect

Kind: anti-pattern

Layer: Enforcement Core

Record: architecture:hidden-side-effect

Severity: discouraged

Scope: event_messaging

Formed by: Make an operation appear like a query or pure function while it mutates state, performs I/O, emits events, or changes global context.

Canonical: Ontology

A defect in which an operation that looks like a query mutates state or performs I/O that its name and signature do not show.

Listed in Architecture principles, after Temporal Coupling and before Action at a Distance.

Refactored by

• Separate Query from Command
• Make Effects Explicit

Severity

• discouraged

Category

• Anti-patterns

Force

• Event messaging

Violates

• Predictability
• Composability
• Principle of Least Surprise
• Controlled Side Effects

Negated by

• Principle of Least Surprise
• Controlled Side Effects

Linked from

• Instruction patterns
• Fail at the boundary
• A system is a graph
• Seven controls, seven classes
• Anti-patterns
• Correctness / Determinism / Verification
• Core Modular Design
• Schema / Canonical Data / Semantics
• Transactions / State / Concurrency
• Core Modular Design
• Correctness / Determinism / Verification
• Severity levels
• The forces