4. Generics & Constraints | Abhimanyu Aryan

Generics with extends constraints ensure type parameters meet a minimum shape.

File: packages/ai/src/types.ts L135-139

export type StreamFunction<TApi extends Api = Api, TOptions extends StreamOptions = StreamOptions> = (
  model: Model<TApi>,
  context: Context,
  options?: TOptions
) => AssistantMessageEventStream;

TApi extends Api — constraint: must be an API type
= Api — default: falls back to the base Api when not specified
TOptions extends StreamOptions — the options must at least satisfy StreamOptions

File: packages/ai/src/api-registry.ts L66-68

export function registerApiProvider<TApi extends Api, TOptions extends StreamOptions>(
  provider: ApiProvider<TApi, TOptions>,
  sourceId?: string,
): void { ... }

Multi-parameter generics with constraints on both type parameters.