@ue-too/being / createStateGuard

Function: createStateGuard()

createStateGuard<T>(set): (s) => s is T

Defined in: interface.ts:1022

Creates a type guard function for checking if a value belongs to a specific set of states.

Type Parameters

T

T extends string

String literal type to guard for

Parameters

set

readonly T[]

Readonly array of string literals defining the valid states

Returns

A type guard function that checks if a string is in the set

(s): s is T

Parameters

s

string

Returns

s is T

Remarks

This utility function generates a TypeScript type guard that narrows a string type to a specific union of string literals. Useful when you have multiple state types and need to distinguish between them at runtime.

Example

Creating state guards for hierarchical state machines

type MainStates = "idle" | "active" | "paused";
type SubStates = "loading" | "processing" | "complete";
type AllStates = MainStates | SubStates;

const MAIN_STATES = ["idle", "active", "paused"] as const;
const isMainState = createStateGuard(MAIN_STATES);

function handleState(state: AllStates) {
  if (isMainState(state)) {
    // TypeScript knows state is MainStates here
    console.log('Main state:', state);
  } else {
    // TypeScript knows state is SubStates here
    console.log('Sub state:', state);
  }
}