/**
 * @description Extracts all non-undefined types from a union type T.
 * @template T The union type.
 */
type NonUndefined<T> = T extends undefined ? never : T;

// --- Usage Example ---
type MixedValue = string | number | undefined | boolean;

type OnlyDefined = NonUndefined<MixedValue>;
// Expected: string | number | boolean

const val1: OnlyDefined = 'hello';
const val2: OnlyDefined = 123;
const val3: OnlyDefined = true;
// const val4: OnlyDefined = undefined; // Type error: Type 'undefined' is not assignable to type 'OnlyDefined'.

type NullableString = string | null | undefined;
type NonNullableAndNonUndefinedString = NonUndefined<NullableString>;
// Expected: string | null

// Combine with TypeScript's NonNullable for strict definition
type StrictDefined<T> = NonUndefined<NonNullable<T>>;
type StrictString = StrictDefined<NullableString>;
// Expected: string