Has the unsoundness (will explain in the post) actually become a pitfall in practice?

• sum-types

  2 39 0.0 TypeScript

  Safe, ergonomic, non-generic sum types in TypeScript.

  

  Anywhere that overloads are needed will rely upon type assertions or the unsafety implicit in overloads, for example in fp-ts/function::pipe. It'll come up a lot with objects too when there isn't a preexisting primitive you can compose atop of, as in for example fp-ts-std/Record::pick. Something as generic as @unsplash/sum-types has assertions all over the place, though to be fair that's mostly again a case of struggles interacting with object types.

• TypeScript

  444 91,617 9.9 TypeScript

  TypeScript is a superset of JavaScript that compiles to clean JavaScript output.

  

  I think this feature might finally be coming in the near future! It's mentioned in the 4.6 iteration plan (https://github.com/microsoft/TypeScript/issues/46858) and a few design meeting notes!

• Klotho

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• Visual Studio Code

  1,015 146,870 10.0 TypeScript

  Visual Studio Code

  

  As for the strange behavior around type variance, there are some good and some interesting reasons strictFunctionTypes only applies in limited cases. The original release blog post explains these reasons quite well, using relatively simple terms. To oversimplify, TS can't perfectly represent certain JS cases without significantly sacrificing performance and usability or making massive breaking changes. Interestingly, even strictFunctionTypes, which only affects a small subset of functions, caused 800 compile errors when VSCode enabled it.

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