37 lines
906 B
TypeScript
37 lines
906 B
TypeScript
/**
|
|
* Helper function for exhaustive checks of discriminated unions.
|
|
* https://basarat.gitbooks.io/typescript/docs/types/discriminated-unions.html
|
|
*
|
|
* @example
|
|
*
|
|
* type A = {type: 'a'};
|
|
* type B = {type: 'b'};
|
|
* type Union = A | B;
|
|
*
|
|
* function doSomething(arg: Union) {
|
|
* if (arg.type === 'a') {
|
|
* return something;
|
|
* }
|
|
*
|
|
* if (arg.type === 'b') {
|
|
* return somethingElse;
|
|
* }
|
|
*
|
|
* // TS will error if there are other types in the union
|
|
* // Will throw an Error when called at runtime.
|
|
* // Use `assertNever(arg, true)` instead to fail silently.
|
|
* return assertNever(arg);
|
|
* }
|
|
*/
|
|
export function assertNever(value: never, noThrow?: boolean): never {
|
|
if (noThrow) {
|
|
return value
|
|
}
|
|
|
|
throw new Error(
|
|
`Unhandled discriminated union member: ${JSON.stringify(value)}`,
|
|
);
|
|
}
|
|
|
|
export default assertNever;
|