api-types-problem.ts

import * as t from 'io-ts';
function request<P extends t.Props>(type:string, props:P) {
  return t.type({
    type: t.literal(type),
    props: t.type(props)
  });
}
export const RequestT = t.union([
  request('foo', {
    baz: t.string,
    quux: t.array(t.string)
  }),
  request('bar', {
    a: t.number,
    b: t.string
  })
]);
export type Request = t.TypeOf<typeof RequestT>;
function f(r:Request) {
  switch(r.type) {
    case 'foo':
      console.log(r.props.baz);
  }
}
  /*
  test.ts:22:27 - error TS2339: Property 'baz' does not exist on type 'TypeOfProps<{ baz: StringType; quux: ArrayType<StringType, string[], string[], mixed>; }> | TypeO...'.
  Property 'baz' does not exist on type 'TypeOfProps<{ a: NumberType; b: StringType; }>'.

22       console.log(r.props.baz);

  */