I would still have a full head of hair if this had been the case since the beginning. Nonetheless I am glad that we got here in the end.

type Dog = { bark: () => void }

type Cat = { meow: () => void }

function speak(animal: Dog | Cat) {

    if (‘bark’ in animal) {

        animal.bark();

    } else {
        animal.meow();
    }

Okay, okay, I know you can filter using ‘in’ to see if it has methods, but in real life, in a company where you have a colleague (who is a golden boy) who writes over-engineered code with hundreds of interfaces of interfaces, you don’t want to spend time searching through the files to find every element that is in the union type.

Whereas in Rust it does:

struct Dog { name: String, }

struct Cat { name: String, }

enum Animal {

    Dog(Dog),

    Cat(Cat),

fn process_animal(animal: Animal) {

    match animal {

        Animal::Dog(dog) => {

            println!(‘It is a dog named {}’, dog.name);

        }

        Animal::Cat(cat) => {

            println!(‘It is a cat named {}’, cat.name);

        }
    }

I think TypeScript should add a couple of lines of code to the generated JavaScript to do something like:

type Dog = { bark: () => void }

type Cat = { meow: () => void }

function speak(animal: Dog | Cat) {

    if (animal is Dog) {

        animal.bark();

    } else {

        animal.meow();

    }
}

Though TypeScript 7.0 will be significant in that it will use the new Go compiler

On the other hand, I can understand leaving it as the last thing to do, after the foundation has set. Also, the TypeScript team has really done an amazing job all these years with backward compatibility, so that is extremely reassuring.

Maybe my uneasiness is just impatience to get to use the sped-up version in my app as well! :)

Now when .NET team complains about adoption I get to point out Typescript 7's contribution repo.

And yes I know the reasons, my nick is on the discussions, please also watch the BUILD session where they acknowledge having to rewrite the whole datastructures due to Go's weaker type system.

It would have been an affront to have a 6.0 that shipped without the means to work for so so many javascript frameworks/libraries. AlCalzone utterly saving the day.

I also am so so so thankful that maybe perhaps after what felt like a never ending dolldrums, we may finally be getting decorator support in some browsers. What a colossal relief it will be to see the progress of the language become manifest.