8 ms·

TypeScript 4.4 Beta

63 points by bpierre 5y ago

adamddev1 5y ago
I'm very happy to see the inclusion of "Control Flow Analysis of Aliased Conditions." This has been something I have been wishing for for awhile now and a delight to see it come out in this release. TypeScript just keeps getting better and better.
- blacktriangle 5y ago
  Interesting, is this a new-ish idea in type systems? The first time I saw something similar was in Kotlin as a technique for dealing with null checks without having to rename the unwrapped variable. Are there other languages that have this feature?
  - milliams 5y ago
    I think that Python's type checkers do this sort of thing now, e.g. via TypeGuard (https://www.python.org/dev/peps/pep-0647/ https://www.python.org/dev/peps/pep-0647/)
    - iso8859-1 5y ago
      That's a PEP for Python 3.10, which isn't even released yet. And Mypy only supports it since May: https://github.com/python/mypy/issues/5206#issuecomment-844144556 https://github.com/python/mypy/issues/5206#issuecomment-8441...
  - ajanuary 5y ago
    I first saw it in Typed Racket under the name "Occurrence typing" [1]. It's not a coincidence that Typed Racket is also a type system applied retroactively to a dynamically typed language. The first mention of "occurrence typing" in scheme I can find is a 2008 paper [2] [1] https://docs.racket-lang.org/ts-guide/occurrence-typing.html https://docs.racket-lang.org/ts-guide/occurrence-typing.html [2] https://www2.ccs.neu.edu/racket/pubs/popl08-thf.pdf https://www2.ccs.neu.edu/racket/pubs/popl08-thf.pdf
    - muglug 5y ago
      TypeScript doesn't do proper occurrence typing: https://www.typescriptlang.org/play?ts=4.4.0-beta#code/GYVwdgxgLglg9mABMOcAUBDAXIgzlAJxjAHMAfMEAGyoBpEAjHfI0i6qgSmcOJMQDeAWABQicYhjBEmRAF4FiSjUQAyVY3mLlXQaIkHEBAKZQQBJAHIAJseAZqUSwG59EgL6i34qTIyIAQm0OTj0xQ3ETMwtEDFdw8U8RbyNTcyQGePcgA https://www.typescriptlang.org/play?ts=4.4.0-beta#code/GYVwd... Compare to Typed Racket: #lang typed/racket (: foo (-> (U String Null) (U String Null) String)) (define (foo a b) (cond [(and (null? a) (null? b)) "default"] [(not (null? a)) a] [#t b])) Or Psalm, a PHP typechecker I created with occurrence typing: https://psalm.dev/r/60ef4c299e https://psalm.dev/r/60ef4c299e
- SavantIdiot 5y ago
  Me too. Especially no longer having to explain to TS in many places that "yes, I already checked this type!" EDIT: What I'd like to see now is a "cleanup" hint, which says: hey I already know what type this is, you can remove these 10 lines of aliasing code in this function.
- eyelidlessness 5y ago
  I agree this is a huge improvement. It addresses one of the few remaining cases where the anti-TS crowd could rightly claim embracing the type system leads to more convoluted code than JS.
typescriptual 5y ago
From time to time I come across amazing things made with seemingly advanced type system of typescript (eg. sql engine). What is the trail I should follow if I want learn how to do such things?
- ldlework 5y ago
  Try http://type-tetris.ldlework.com http://type-tetris.ldlework.com :)
goto11 5y ago
Does TypeScript have the most complex and advanced type system ever?
- mariodiana 5y ago
  This is a compound question, since complexity and advancement are two separate issues.
- paulddraper 5y ago
  "Advanced" is debatable, but yes to "complex". At least, in the core language itself, not counting extensions (otherwise Haskell). EDIT: I will say that it is a pleasant surprise how flexible and practical TypeScript's type system is. It would seem that the pressure of working for existing untyped programming patterns has produced something that is very usable and unobtrusive.
- sime2009 5y ago
  No, Scala does.
- sp33der89 5y ago
  I've read a lot online that Scala is complex, but I had an easier time with learning Scala than I had reading through the TypeScript docs. And I dived into TS after Scala. Except for implicits ha.
- ParoxysmalVigor 5y ago
  TS is the most ergonomic and flexible type system i worked with. It has some deep quirks, but end-user app developers rarely have to do anything with those. Miss it a lot when i have to push some python or golang code.
- pornel 5y ago
  It depends how you interpret these things. On a technical level, TS is not sound (you can have runtime type errors in programs that have "correct" types according to TS). For type system aficionados that may not even count as a proper type system.

63 points by bpierre 5y ago

I'm very happy to see the inclusion of "Control Flow Analysis of Aliased Conditions." This has been something I have been wishing for for awhile now and a delight to see it come out in this release. TypeScript just keeps getting better and better.

blacktriangle 5y ago
Interesting, is this a new-ish idea in type systems? The first time I saw something similar was in Kotlin as a technique for dealing with null checks without having to rename the unwrapped variable. Are there other languages that have this feature?
- milliams 5y ago
  I think that Python's type checkers do this sort of thing now, e.g. via TypeGuard (https://www.python.org/dev/peps/pep-0647/ https://www.python.org/dev/peps/pep-0647/)
  - iso8859-1 5y ago
    That's a PEP for Python 3.10, which isn't even released yet. And Mypy only supports it since May: https://github.com/python/mypy/issues/5206#issuecomment-844144556 https://github.com/python/mypy/issues/5206#issuecomment-8441...
- ajanuary 5y ago
  I first saw it in Typed Racket under the name "Occurrence typing" [1]. It's not a coincidence that Typed Racket is also a type system applied retroactively to a dynamically typed language. The first mention of "occurrence typing" in scheme I can find is a 2008 paper [2] [1] https://docs.racket-lang.org/ts-guide/occurrence-typing.html https://docs.racket-lang.org/ts-guide/occurrence-typing.html [2] https://www2.ccs.neu.edu/racket/pubs/popl08-thf.pdf https://www2.ccs.neu.edu/racket/pubs/popl08-thf.pdf
  - muglug 5y ago
    TypeScript doesn't do proper occurrence typing: https://www.typescriptlang.org/play?ts=4.4.0-beta#code/GYVwdgxgLglg9mABMOcAUBDAXIgzlAJxjAHMAfMEAGyoBpEAjHfI0i6qgSmcOJMQDeAWABQicYhjBEmRAF4FiSjUQAyVY3mLlXQaIkHEBAKZQQBJAHIAJseAZqUSwG59EgL6i34qTIyIAQm0OTj0xQ3ETMwtEDFdw8U8RbyNTcyQGePcgA https://www.typescriptlang.org/play?ts=4.4.0-beta#code/GYVwd... Compare to Typed Racket: #lang typed/racket (: foo (-> (U String Null) (U String Null) String)) (define (foo a b) (cond [(and (null? a) (null? b)) "default"] [(not (null? a)) a] [#t b])) Or Psalm, a PHP typechecker I created with occurrence typing: https://psalm.dev/r/60ef4c299e https://psalm.dev/r/60ef4c299e
SavantIdiot 5y ago
Me too. Especially no longer having to explain to TS in many places that "yes, I already checked this type!" EDIT: What I'd like to see now is a "cleanup" hint, which says: hey I already know what type this is, you can remove these 10 lines of aliasing code in this function.
eyelidlessness 5y ago
I agree this is a huge improvement. It addresses one of the few remaining cases where the anti-TS crowd could rightly claim embracing the type system leads to more convoluted code than JS.

typescriptual 5y ago

From time to time I come across amazing things made with seemingly advanced type system of typescript (eg. sql engine). What is the trail I should follow if I want learn how to do such things?

ldlework 5y ago
Try http://type-tetris.ldlework.com http://type-tetris.ldlework.com :)

goto11 5y ago

Does TypeScript have the most complex and advanced type system ever?

mariodiana 5y ago
This is a compound question, since complexity and advancement are two separate issues.
paulddraper 5y ago
"Advanced" is debatable, but yes to "complex". At least, in the core language itself, not counting extensions (otherwise Haskell). EDIT: I will say that it is a pleasant surprise how flexible and practical TypeScript's type system is. It would seem that the pressure of working for existing untyped programming patterns has produced something that is very usable and unobtrusive.
sime2009 5y ago
No, Scala does.
sp33der89 5y ago
I've read a lot online that Scala is complex, but I had an easier time with learning Scala than I had reading through the TypeScript docs. And I dived into TS after Scala. Except for implicits ha.
ParoxysmalVigor 5y ago
TS is the most ergonomic and flexible type system i worked with. It has some deep quirks, but end-user app developers rarely have to do anything with those. Miss it a lot when i have to push some python or golang code.
pornel 5y ago
It depends how you interpret these things. On a technical level, TS is not sound (you can have runtime type errors in programs that have "correct" types according to TS). For type system aficionados that may not even count as a proper type system.