MUmunificent·Feb 15, 2017
TypeScript has some really cool type system features. Union and intersection types are fun and really handy when interacting with dynamically typed code. (If you go back through history, you'll find almost every language with union types also has a mixture of static and dynamic typing. See: Pike, Typed Racket, etc.)
Self types (the "this" in the return type) is handy.
I can see us adding some of those to Dart eventually.
Non-nullable types are great, which I've said for a very long time[1]. We are finally working to try to add them into Dart[2]. It's early still, but it looks really promising so far. It kills me that I've been saying we should do them for Dart since before TypeScript even existed and still they beat us to the punch, but hopefully we can at least catch up.
The main difference between TypeScript and Dart's type systems (and
Read the rest
by the latter I mean strong mode[3], not the original optional type system) is that Dart's type system is actually sound.
This means a Dart compiler using strong mode can safely rely on the types being correct when it comes to dead code elimination, optimization, etc. That is not the case with TypeScript and at this point will likely never be. There is too much extant TypeScript code and JS interop is too important for TypeScript to take the jump all the way to soundness. They gain a lot of ease of adoption from soundness, but they give up some stuff too.
In addition to the above, it means they'll have a hard time hanging new language features on top of static types because the types can be wrong. With Dart, we have the ability to eventually support features like extension methods, conversions, etc. and other things which all require the types to be present and correct.
[1]: http://journal.stuffwithstuff.com/2011/10/29/a-proposal-for-...
[2]: https://github.com/dart-lang/sdk/pull/28619
[3]: https://github.com/dart-archive/dev_compiler/blob/master/STR...