Pure Function
A pure function always returns the same output for the same input and has no side effects — the foundation of functional programming and reliable code.
Purpose
Predictable, testable, cacheable functions that eliminate hidden state dependencies.
Mechanism
Conditions: 1) same input → same output (referential transparency); 2) no side effects (no mutating external state, no depending on mutable external state). Enables memoization, parallel execution, and equational reasoning.
Use cases
- Functional programming
- Simplified testing
- Reliable code