Suggestion Thread: types to add in the future

[ForwardFeed]

I intend to use this issue as a sticky note to hold all ideas of type I had but which I, or someone else will introduce in a later date.
(as I currently write this, the bottleneck of the project isn't the lack of types, but the the lack of testing existing type)

• Static List Length constraint
  StaticListLengthConstaint<T, 5> // T must be of length 5
  useful for specific tuple types

• List No Duplicate
  ListNoDuplicate<[1, false, true, 1]> // fails because one is being duplicated.
  useful to imitate a set, but at compile time

• List No Missing Type
  ListNoMissingType<['key_a', 'key_c'], 'key_a' | 'key_b' | 'key_c'> // fails because ['key_a', 'key_c'] misses 'key_b'
  useful combined to ListNoDuplicate to make a reorder array while ensuring that all element of the array order have been kept

[komed3]

The types mentioned above have been implemented in list.d.ts.

Another type - RequireExactlyOneFrom - has been added to constraints.d.ts:

type RequireExactlyOneFrom< T, K extends keyof T > = RequireExactlyOne< Pick< T, K >, K >;

type Result = RequireExactlyOneFrom<
  { value?: string; values?: string[]; range?: number; },
  'value' | 'values'
>;

// { value: string; values?: never } | { value?: never; values: string[] }

Applies a mutually exclusive constraint to a selected subset of fields without carrying the remaining properties from the source type. This is useful when the source type includes additional fields that should not be part of the exact-one union.