No bare as casts
Any bare as in production TypeScript is a signal to stop and work through the decision tree below. Test files (*.test.ts, *.test-d.ts, test/**/*.ts) are exempt — tests use as for stubbing and type assertions and that's fine.
Decision tree
Work through these in order before writing or keeping a cast:
- Tighten the input type. Can the parameter, generic bound, or return type at the source be made more specific so the cast is unnecessary?
- Add a runtime check. Can a type predicate (
function isUser(x): x is User) narrow the type at runtime, eliminating the cast?
- Restructure a generic. Can a bound or constraint carry the needed information, making the cast unnecessary?
- Use
satisfies. expr satisfies T checks the type without coercing it and is unaffected by this rule. Prefer it when you want a type-check, not a coercion.
- Use
castAs<T>(value). When the value already satisfies T and the assertion is purely declarative, castAs is the right form.
- Only if none of the above: use
blindCast<T, "Reason">(value). The Reason literal must name the specific compromise in language a reviewer can evaluate.
Import
import { blindCast, castAs } from '@internal/utils/casts';
Helper signatures
// Escape hatch — the value is genuinely opaque or unrelated to the target type.
// The Reason literal documents the compromise; the reviewer evaluates it.
function blindCast<TargetType, Reason extends string>(input: unknown): TargetType
// Declarative assertion — the value already satisfies T at runtime.
function castAs<T>(value: T): T
The Reason bar
blindCast is the auditable escape hatch of last resort — not a convenience wrapper. Reach for it only after the decision tree above has been exhausted. The second type argument must be a string literal that a reviewer can act on:
// ✅ Names the specific constraint
blindCast<User, "deserialized from contract validator; shape has already been checked">(raw)
// ❌ Adds no information — reviewer has nothing to evaluate
blindCast<User, "trust me">(raw)
A vague reason is the reviewer's signal to push back and the author's signal to revisit the type design.
"Convert when you touch"
When you touch a file that contains a bare as cast — even as part of unrelated work — convert it to one of the accepted forms or eliminate it. The CI ratchet (pnpm lint:casts) rejects per-PR cast-count increases; converting on contact is how the total comes down over time.