René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Design Meeting Notes, 4/30/2024","articleBody":"\r\n# `TReturn` and `TYield` for Iterators and Other Types\r\n\r\n#58243\r\n\r\n* `TReturn` is the type of values *returned* by a generator.\r\n* `TYield` is the type of values *yielded* by a generator.\r\n* When we added these, we only added them to certain types like `IteratorResult`\r\n    * Since then, we have a PR that adds type parameters to `Iterator`, `IterableIterator`, `AsyncIterable`, etc.\r\n    * What this has meant since then was that if you ever try to grab `value` off of most `IteratorResult`s, then you'll get `any`.\r\n        * Good as a fall-back, but usually not what people want.\r\n* Changing this is a breaking change - so how can we avoid breaks?\r\n    * First, each of these types should have a default value for `TReturn` and `TYield` that is `any`.\r\n        * But when a user writes `Iterator\u003cnumber\u003e`, TypeScript should preserve that type as-is.\r\n    * What is the level of breakage as is?\r\n        * Almost every case is an example of the type system not knowing that `size \u003e 0` implies `value` is not `undefined`.\r\n        * There's also a lot of breakage around DefinitelyTyped's `ExpectType` and `ExpectError` utility types.\r\n* Several new errors introduced. Previously, people expecting `.next()` to return a `T` now get `T | void`.\r\n    * e.g. `if (something.size === 1) { something.values().nexT().value.getTasks(); }`\r\n    * Why is it `void` and not `undefined`?\r\n        * Should it be `undefined`?\r\n        * We really don't want to relitigate all the issues around non-returning functions returning `void` instead of `undefined`.\r\n        * It's possible we carve things out for generators.\r\n    * Should we allow postfix `!` to get rid of `void`?\r\n* How many upvotes does resolution for this issue have?\r\n    * Old issue had around 15 upvotes.\r\n    * This is so breaky that most of this has to go under a switch.\r\n* What happens if we don't do this?\r\n    * People trying to thread these into the built-in iterator types.\r\n    * If you have a generator, you can now write `myGenerator().map(x =\u003e x * x)` and you want the `TReturn` preserved.\r\n* If the worst thing you have to do is add a `!`, is that so bad?\r\n* Feel like there should be an approach where this is flagged.\r\n    * Could be like `strictBindCallApply`.\r\n    * We fret about breaks for much more widely-requested features.\r\n    * But the people it breaks are using iterators, probably want to use the feature.\r\n    * The flag that this conceptually aligns with is `noUncheckedIndexedAccess`.\r\n        * Ah yes, `.next()`, the famous indexed access syntax.\r\n        * Okay, fine, a separate flag with an equally bad name (`noUncheckedIteratorAccess` or `noUncheckedIteratorResult`).\r\n\r\n# `tsc --init` Updates?\r\n\r\n* We noticed `tsc --init` adds `\"module\": \"commonjs\"` - which our docs said to never ever ever do.\r\n* Okay, what else do we need to fix in `--init`?\r\n* [Ryan asked on Twitter what people would like to change](https://twitter.com/SeaRyanC/status/1782783901213282557).\r\n* People said lots of stuff\r\n    * Big one that resonates: remove the wall of text comments\r\n* Are we okay wiht `tsc --init` generating a file today?\r\n    * Uh yes.\r\n* Okay, that's a good start.\r\n* What else?\r\n    * Make it minimal\r\n    * People seem opposed to interactive.\r\n* Okay, what are things that need to be hashed through?\r\n    * `target: esnext`?\r\n    * `module` - `node16` or `bundler`?\r\n    * `verbatimModuleSyntax`?\r\n    * `skipLibCheck`?\r\n    * We need to hash through these.\r\n* Should we still have *some* comments on defaults?\r\n    * Maybe.\r\n    * [Ryan also wrote a wizard](https://ryancavanaugh.github.io/tsc-init/), someone else wrote something too.","author":{"url":"https://github.com/DanielRosenwasser","@type":"Person","name":"DanielRosenwasser"},"datePublished":"2024-05-02T22:14:23.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/58417/TypeScript/issues/58417"}