Type Variance Example

contravariance_example.ts

interface Animal {
  name: string;
}

interface Cat extends Animal {
  meow: () => void;
}

function doMeow(cat: Cat) {
  cat.meow();
}

function sayName(a: Animal) {
  console.log(a.name);
}

const cat: Cat = {
  name: "Sir cat",
  meow: () => console.log("Meow!")
}

doMeow(cat)

function handleCat(cat: Cat, callback: (a: Cat) => void) {
  callback(cat);
}

function handleAnimal(cat: Cat, callback: (a: Animal) => void) {
  callback(cat);
}

handleCat(cat, doMeow);
handleCat(cat, sayName);

handleAnimal(cat, doMeow);
handleAnimal(cat, sayName);

TS Playground link:
https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgIImAWzgG2QbwFgAoZZEOTCALmQGcwpQBzAbhIF8STRJZEUAYThhkEAB6QQAEzpoM2PEVLIqAewDutABQBKZAF4AfMgBua4NPbEuxEjACuIBGGBqQyaWoCyETdoQRWmEwfWUyQLAAOnUNPWtbeycXNw86OABPADlKCG04WnQsXDCSCPc6NRwIKJw1ZnyoiipdBO5iBArRSOCRQwIy8lzaACIAZWAoZEiRgBpB2J19Y2mKqpq6hpHfTQBCEd1Odq8duMjDu2JHZ1d3ZAALOBlqkICg5BDZ6dwcACNEADWOgKHxEyxM5kspRUgRwf0Bb1CbUu1xSd0ezwgRUUiN6YC+sPhCCByHyhQUJUMEIs0mhER+-2JiNaR0uGOkLxEiK+Jz8GhZxHZnLA3PomRyLWsJCFWIpOFFvM0Apl2NwovS2VyAqAA