kek.ts

gistfile1.txt

/**
 * Type the `filterTable` function to take a Table,
 * a list of column names, and to return a table that
 * only contains columns with these names.
 */
type FilterTable<Table, NameUnion> = TODO;

declare type UserTable = [
  { name: 'firstName'; values: string[] },
  { name: 'lastName'; values: string[] },
  { name: 'age'; values: number[] },
];

type res1 = FilterTable<UserTable, 'age'>;
type res2 = FilterTable<UserTable, 'firstName' | 'lastName'>;
type res3 = FilterTable<UserTable, 'firstName' | 'age'>
type res4 = FilterTable<UserTable, ''>

type FilterTable<Table, NameUnion> = Table extends [infer R, ...infer Rest]
    ? R extends { name: NameUnion }
      ? [R, ...FilterTable<Rest, NameUnion>]
      : FilterTable<Rest, NameUnion>
    : [];
    ```