| // Helper type. Not useful on its own. |
| type Without<FirstType, SecondType> = {[KeyType in Exclude<keyof FirstType, keyof SecondType>]?: never}; |
| |
| /** |
| Create a type that has mutually exclusive properties. |
| |
| This type was inspired by [this comment](https://github.com/Microsoft/TypeScript/issues/14094#issuecomment-373782604). |
| |
| This type works with a helper type, called `Without`. `Without<FirstType, SecondType>` produces a type that has only keys from `FirstType` which are not present on `SecondType` and sets the value type for these keys to `never`. This helper type is then used in `MergeExclusive` to remove keys from either `FirstType` or `SecondType`. |
| |
| @example |
| ``` |
| import {MergeExclusive} from 'type-fest'; |
| |
| interface ExclusiveVariation1 { |
| exclusive1: boolean; |
| } |
| |
| interface ExclusiveVariation2 { |
| exclusive2: string; |
| } |
| |
| type ExclusiveOptions = MergeExclusive<ExclusiveVariation1, ExclusiveVariation2>; |
| |
| let exclusiveOptions: ExclusiveOptions; |
| |
| exclusiveOptions = {exclusive1: true}; |
| //=> Works |
| exclusiveOptions = {exclusive2: 'hi'}; |
| //=> Works |
| exclusiveOptions = {exclusive1: true, exclusive2: 'hi'}; |
| //=> Error |
| ``` |
| */ |
| export type MergeExclusive<FirstType, SecondType> = |
| (FirstType | SecondType) extends object ? |
| (Without<FirstType, SecondType> & SecondType) | (Without<SecondType, FirstType> & FirstType) : |
| FirstType | SecondType; |
| |