ts-extras/distribution/array-concat.d.ts

Essential utilities for TypeScript projects

/**
A strongly-typed version of `Array#concat()` that properly handles arrays of different types.

TypeScript's built-in `Array#concat()` has issues with type inference when concatenating arrays of different types or empty arrays. This function provides proper type inference for heterogeneous array concatenation.

Note: This function preserves array holes, matching the native `Array#concat()` behavior.

@example
```
import {arrayConcat} from 'ts-extras';

const strings = ['a', 'b'];
const numbers = [1, 2];

// TypeScript's built-in concat would error here
const mixed = arrayConcat(strings, numbers);
//=> ['a', 'b', 1, 2]
//   ^? (string | number)[]

// Works with tuples
const tuple = arrayConcat(['x'] as const, [1] as const);
//=> ['x', 1]
//   ^? (1 | 'x')[]

// Handles empty arrays correctly
const withEmpty = arrayConcat([], ['hello']);
//=> ['hello']
//   ^? string[]
```

@category Improved builtin
*/
export declare function arrayConcat<T extends readonly unknown[]>(array: T): T extends ReadonlyArray<infer U> ? U[] : never;
export declare function arrayConcat<T extends readonly unknown[], U extends ReadonlyArray<readonly unknown[]>>(array: T, ...items: U): ArrayConcatUnlimited<T, U> extends ReadonlyArray<infer R> ? R[] : unknown[];
type ArrayConcatUnlimited<First extends readonly unknown[], Rest extends ReadonlyArray<readonly unknown[]>> = Rest extends readonly [
    infer Next extends readonly unknown[],
    ...infer Remaining extends ReadonlyArray<readonly unknown[]>
] ? ArrayConcatUnlimited<[...First, ...Next], Remaining> : First;
export {};