Specifications

The Specification pattern expresses composable business rules as predicates over candidate objects.

A Specification encapsulates a rule evaluated with is_satisfied_by(candidate). Compositions (&, |, ~) allow rules to be combined into richer predicates.

When to use

Subclass Specification and implement is_satisfied_by(candidate) → bool. Compose with &, |, ~ instead of nesting if-statements. Each specification is a single, testable unit of logic.

Where the implementation lives

The specification pattern is defined in the Foundation block because composable predicates are reusable outside the Domain block. The Domain block re-exports it.