Non-empty array type
Encode "at least one element" in the type so head, max and similar functions never see an empty array.
- TypeScript
- GreenSnippets
- MIT
- Executed with Node.js 22 (type stripping)
type NonEmptyArray<T> = [T, ...T[]];
function isNonEmpty<T>(array: readonly T[]): array is NonEmptyArray<T> {
return array.length > 0;
}
function maxOf(numbers: NonEmptyArray<number>): number {
return Math.max(...numbers);
}
function first<T>(array: NonEmptyArray<T>): T {
return array[0];
}Example / expected output
const scores = getScores(); // number[]
if (isNonEmpty(scores)) console.log(maxOf(scores));How it works
Instead of checking for empty arrays at runtime everywhere, make the invalid state unrepresentable. The tuple type [T, ...T[]] guarantees an element at index 0. A small guard converts ordinary arrays when you need to.
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