Core Concepts
The library applies the Specification Pattern: a small rule evaluates a candidate, and larger rules are built by composing those values. Rust’s trait system makes the static path the default; dynamic dispatch, heap allocation, and thread sharing are explicit choices.
Static and dynamic rules
Choose the smallest boundary that matches the problem:
| Need | Rust type | Cost and guarantee |
|---|---|---|
| Known rules composed at compile time | And, Or, Not | No library allocation or trait-object dispatch |
| Homogeneous collection | AllOf, AnyOf | Borrows a slice and short-circuits |
| Heterogeneous/runtime-selected rules | BoxedSpecification<T> | Owns a Box<dyn Specification<T>> |
| Rule shared between threads | SharedSpecification<T> | Owns an Arc and requires Send + Sync + 'static |
use specification_core::{BoxedSpecification, Specification};
let rules: Vec<BoxedSpecification<u64>> = vec![
BoxedSpecification::new(|value: &u64| *value > 0),
BoxedSpecification::new(|value: &u64| *value % 2 == 0),
];
assert!(rules[1].is_satisfied_by(&42));The complete thread-sharing scenario is in
dynamic_and_concurrency.rs.
Boolean identities and short-circuiting
and, or, and not preserve left-to-right short-circuit evaluation. An
empty AllOf is true, and an empty AnyOf is false. These identities let
an application construct a rule from a possibly empty collection without
special-case control flow.
Typed decisions
FirstMatch<T, Decision> is the explicit dynamic boundary for ordered routing.
It stores heterogeneous rules with one concrete decision type, evaluates them
in insertion order, and returns the first matching Option<&Decision>. Use
decide_or when a fallback is required. See Decisions and Evaluation
Context for a complete route-selection
example.
Immutable context and dependencies
EvaluationContext<UserData> is an immutable input snapshot. Application data
is typed through UserData; counters, flags, and timestamps have deliberate
defaults. Time rules receive a Clock explicitly, so FixedClock can make a
boundary deterministic in tests. There is no global context registry.
See Concurrency Contracts for Send + Sync behavior and
Decisions and Evaluation Context for the
built-in rules.
The runtime-neutral async layer is described in Async Specifications. Optional wire-format and predicate-macro support are described in Serialization and Macros.