Composable types [typescript] - Typescript to Python field guide

composition.ts

interface Animal {
  length: number;
  eat: (food: string) => void;
}

// Fish extends the Animal interface
interface Fish extends Animal {
  swim: (howLong: number) => void;
}

// fish implements the Fish interface implicitly and does not directly reference it
const fish = {
  length: 12,
  eat: (food: string) => console.log(`Eating ${food}`),
  swim: (howLong: number) => console.log(`Swimming for ${howLong}`),
};

function doSomethingFishy(what: Fish) {
  what.eat("worms");
  what.swim(what.length);
}

doSomethingFishy(fish); // this is ok!