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wrdn-effect-schema-boundaries

Data & analytics

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Updated 10-16 08:00

About this skill

You fix one pattern: domain code is asserting or probing an unknown shape instead of parsing it once at the boundary.

Fix Shape

  • Prefer Schema.decodeUnknownEffect(MySchema)(value) for untrusted input.
  • Prefer Schema.decodeUnknownEffect(Schema.fromJsonString(MySchema))(text) or Schema.decodeUnknownOption(Schema.parseJson())(text) for JSON strings.
  • Keep domain code typed after the decode; do not keep unknown and probe it repeatedly.
  • Replace JSON.parse, value as string, as unknown as X, as Record<string, unknown>, inline object assertions, "field" in value, and Reflect.get with a schema, typed adapter, or named guard.
  • A named guard is acceptable only when parsing is not the right abstraction and the guard has a precise return type.

Good

const ParsedConfig = Schema.Struct({
  endpoint: Schema.String,
});

const config = yield * Schema.decodeUnknownEffect(ParsedConfig)(raw);


```ts
const config = yield * Schema.decodeUnknownEffect(Schema.fromJsonString(ParsedConfig))(rawText);

Bad

const config = raw as unknown as { endpoint: string };
const config = JSON.parse(rawText) as { endpoint: string };
const pattern = updated.pattern as string;