NOT READY TO MERGE - Use conditional type inference for promise resolution#29671

forivall · 2019-01-31T23:16:56Z

This improves the quality of the type resolution for promise constructor
methods, as using conditional type inference is distributive, whereas
the inference provided by arguments is not.

Alternatively, the arguments based inference could be improved, but that
would be a completely different kind of change.

Fixes #

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This improves the quality of the type resolution for promise constructor methods, as using conditional type inference is distributive, whereas the inference provided by arguments is not. Alternatively, the arguments based inference could be improved, but that would be a completely different kind of change.

AlCalzone · 2019-02-01T07:29:57Z

I think we get it @typescript-bot 😂

j-oliveras · 2019-02-01T08:42:42Z

@RyanCavanaugh @DanielRosenwasser I think the bot gone crazy 🤣

forivall · 2019-02-07T22:27:45Z

I discovered how this will be a breaking change: if the user has manually defined their types in the <>, this change will cause a compile error.

I discovered this when i changed one of my own functions from

exportconstfirst=<T>(val: T|ReadonlyArray<T>): T=>Array.isArray(val) ? val[0] : val

to

exportconstfirst=<T>(val: T): TextendsReadonlyArray<infer U> ? U : T=>Array.isArray(val) ? val[0] : val

In some circumstance where I had defined first<string|undefined>(foo /* : string | string[] | undefined */), I had to remove the <string|undefined> for it to work. This was needed before changing the types to use conditionals, as typescript was unable to infer that that was the type needed, with the error

Argument of type 'string | string[] | undefined' is not assignable to parameter of type 'string | ReadonlyArray<string>'. Type 'undefined' is not assignable to type 'string | ReadonlyArray<string>

So, i would propose an improvement to the arguments-based inference to be distributive. Does anyone know if this issue has been reported?

sandersn

@forivall Can you make an issue for this that explains the problem, the solution, and the drawback you discovered? It sounds like there's an associated inference change that's needed, and a PR doesn't seem like the right place for that discussion.

forivall · 2021-11-17T21:03:54Z

Superceded by #45350, #33707

forivall force-pushed the forivall/improve-promise-typings branch from b8a9fd1 to e3522fdCompare January 31, 2019 23:22

RyanCavanaugh added the Experiment A fork with an experimental idea which might not make it into master label Apr 23, 2019

sandersn requested changes Feb 3, 2020
View reviewed changes

forivall mentioned this pull request Feb 6, 2020
"Similar Comments" and "Hidden Items" widgets are poorly displayed DarkThemeHub/GithubDarkTheme#138
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forivall marked this pull request as draft June 29, 2020 19:23

forivall closed this Nov 17, 2021

microsoft locked as resolved and limited conversation to collaborators Oct 21, 2025

NOT READY TO MERGE - Use conditional type inference for promise resolution#29671

NOT READY TO MERGE - Use conditional type inference for promise resolution #29671

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forivall commented Feb 7, 2019•
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