# _CollapseRestElement

`type` in `services` · v0.8.2

<https://docs.seedcord.org/packages/services/0.8.2/types/collapse-rest-element>

## Declaration

```ts
type _CollapseRestElement<TArray extends UnknownArray, ForwardAccumulator extends UnknownArray = [], BackwardAccumulator extends UnknownArray = []> = TArray extends UnknownArray // For distributing `TArray` ? keyof TArray & `${number}` extends never // Enters this branch, if `TArray` is empty (e.g., []), // or `TArray` contains no non-rest elements preceding the rest element (e.g., `[...string[]]` or `[...string[], string]`). ? TArray extends readonly [...infer Rest, infer Last] ? _CollapseRestElement<Rest, ForwardAccumulator, [Last, ...BackwardAccumulator]> // Accumulate elements that are present after the rest element. : TArray extends readonly [] ? [...ForwardAccumulator, ...BackwardAccumulator] : [...ForwardAccumulator, TArray[number], ...BackwardAccumulator] // Add the rest element between the accumulated elements. : TArray extends readonly [(infer First)?, ...infer Rest] ? _CollapseRestElement<Rest, [...ForwardAccumulator, '0' extends OptionalKeysOf<TArray> ? If<IsExactOptionalPropertyTypesEnabled, First, First | undefined> // Add `| undefined` for optional elements, if `exactOptionalPropertyTypes` is disabled. : First], BackwardAccumulator> : never // Should never happen, since `[(infer First)?, ...infer Rest]` is a top-type for arrays. : never
```