[dmix]

> but any time someone saves a Selection into a member variable, they ended up writing down whatever type TS inferred at that time, e.g.

> mySel: d3.Selection<HTMLElement, {}, null, undefined>;

I'm curious how Google and others approach adopting Typescript gradually, as I'm pretty new to it, I'm assuming it goes like: The programmer converts code to Typescript and when they come across return types they copy the inferred type and add it to the codebase directly wherever possible. I'm assuming just as a matter of using (untyped) libraries you need to rely on the output of Typescript in order to try have every return typed.

So the biggest problem seems to be how TS infers things changed meaning you can't always trust what you copied as staying consistent, even if the source library doesn't change itself. That's always something to keep in mind for overhead.

[gmoot]

The explicit type is optional. It's not that it's required to copy out whatever the compiler inferred, it's just that lots of people do it to be explicit.

[dmix]

All types are optional in typescript. I was just curious about Google's approach to it and if they had some standard practice of always copying the inferred type to get a great amount of coverage.

[lonelappde]

Copying the inferred type is the same as copying your runtime outputs into your tests. It's a statement that you believe the result is correct and it's on you to make that judgement call. It's not a policy to blindly copy everything, because that defeats the purpose of type checking and testing, turning your tests into " verify that nothing changed", not "verify that the system behaves as intended".

[dmix]

Thanks, thats typically how I approach it as well, it's good to hear it written out. I try not to append copied types without fully understanding their structure either. But sometimes you just need to just trust it to solve a problem.

There's plenty of blog posts and docs on advanced types but I'm interested in the day-to-day best practical approaches people are taking adopting it. I should look around for some literature or talks on the subject...