@ai-sdk/rsc/src/streamable-value/streamable-value.ts

[React Server Components](https://react.dev/reference/rsc/server-components) for the [AI SDK](https://ai-sdk.dev/docs):

export const STREAMABLE_VALUE_TYPE = Symbol.for('ui.streamable.value');

export type StreamablePatch = undefined | [0, string]; // Append string.

declare const __internal_curr: unique symbol;
declare const __internal_error: unique symbol;

/**
 * StreamableValue is a value that can be streamed over the network via AI Actions.
 * To read the streamed values, use the `readStreamableValue` or `useStreamableValue` APIs.
 */
export type StreamableValue<T = any, E = any> = {
  /**
   * @internal Use `readStreamableValue` to read the values.
   */
  type?: typeof STREAMABLE_VALUE_TYPE;
  /**
   * @internal Use `readStreamableValue` to read the values.
   */
  curr?: T;
  /**
   * @internal Use `readStreamableValue` to read the values.
   */
  error?: E;
  /**
   * @internal Use `readStreamableValue` to read the values.
   */
  diff?: StreamablePatch;
  /**
   * @internal Use `readStreamableValue` to read the values.
   */
  next?: Promise<StreamableValue<T, E>>;

  // branded types to maintain type signature after internal properties are stripped.
  [__internal_curr]?: T;
  [__internal_error]?: E;
};