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0 pointsthejameskyle9y ago0 comments

We've actually been discussing going the other way with a conversion tool for package publishers. Flow has a more sound type system and it's easier to downgrade than upgrade.

The next few months should hopefully start seeing a lot of new tools for managing and publishing types within the community. It would be great to see more adoption from package owners themselves.

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smt889y ago· 2 in thread

> conversion tool for package publishers

I'm not sure I understand how that's different from just supporting TypeScript definitions. Couldn't the conversion tool just be built into Flow so that it works transparently for the user? Or are you saying human intervention is required?

> Flow has a more sound type system

Can you elaborate? What are the features of Flow that aren't present in TypeScript and would result in lossy conversion?

thejameskyleOP9y ago

It's not a trivial task for either Flow or TypeScript to support definitions of one another.

We've attempted to build a TS => Flow conversion tool, but it's much harder to go in that direction because you have less guarantees.

You aren't going to find a lot of "features" that either one supports that the other does not. However, many of TypeScript's implementations of the same features are less strict even with all of the strict flags on.

Here's an example that came up just last week: https://gist.github.com/thejameskyle/24a4e32be4899419e53eec6... (Note: This is not a bug in TypeScript, it's a design decision)

Because Flow is more strict than TypeScript it's much easier to convert from Flow definitions to TypeScript definitions.

thorn0asdf9y ago

It should be much easier to implement a "TS definition source files (.d.ts) => Flow" converter than generic "TS => Flow". The language in .d.ts is a small subset of TS. Are your explanations about Flow's strictness really applicable to this subset?

See https://github.com/Microsoft/TypeScript/blob/master/doc/spec...

> Here's an example that came up just last week: [...] (Note: This is not a bug in TypeScript, it's a design decision)

I believe this design decision isn't final, but again: what difference does this example make if we're talking just about type declarations?

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eyko9y ago

I very much doubt many package publishers will do this. Most users (if not all) that ask for TypeScript definition files support are doing so because they want to take advantage of DefinitelyTyped / @types going forward. However, any tools that can help us write once and use in both Flow and TypeScript will definitely be well received.

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