Simple example to show an issue with array index access.

access.ts

interface IGenericThing {
  bop: [string, string, string];
  [key: string]: string | number | [string, string, string];
}

const foo: IGenericThing = {
  bar: '#0000ff',
  baz: 123,
  bat: ['a', 'b', 'c'],
  bop: ['d', 'e', 'f'],
};

const boo: IGenericThing = {
  bleep: foo.baz,
  bloop: foo.bat[0],
  blergh: foo.bop[0],
}

// `blergh` is fine, but `bloop` will error
// Element implicitly has an 'any' type because type 'string | number | [string, string, string]' has no index signature.