import { isNonNull, assertNonNull } from '@dozerg/condition';

function foo(p?: string) {
  assertNonNull(p);
  p.length; // OK, p is string
  // ...

  const a = [1, undefined, 2];   // a is (number | undefined)[]
  const b = a.filter(isNonNull); // b is [1, 2], i.e. number[]
  // ...
}