From: "zverok (Victor Shepelev)" Date: 2022-08-30T07:07:08+00:00 Subject: [ruby-core:109782] [Ruby master Feature#18980] Re-reconsider numbered parameters: `it` as a default block parameter Issue #18980 has been updated by zverok (Victor Shepelev). > It's interesting that "Numbered parameters (_1, _2, ...) look like unused local variables" doesn't seem to resonate with you. It did initially, but let's say I got over it. There were several factors in play: 1. I am very concerned about readability and brevity, but I actually don't believe _any_ "core" name choice makes something "totally unreadable". Syntax structures might, but names are just sigils you soon get used too. Say, I considered `yield_self` so wrong naming choice I spent the good part of that year fighting for its renaming, but at the same time I started to use it (and it DID make code better, as my colleagues agreed, you just needed to get used to the weird name). I frequently call for name compromises (let's stop on _one_ name and move forward instead of five more years of discussion). 2. At the moment of introduction of numbered args, I was more concerned that it is a _principally_ wrong feature (it somewhat overshadowed the idea of shortening blocks with method references, with method references then being dropped altogether). But then I tried it reluctantly and turned out it made life much easier. 3. In practice, it was really easy to get used to. `_1` is easy to remember and recognize in others' code. And I never met code that uses `_1` before (and rarely the code that uses `_l`, TBH), so it wasn't like I really needed to rewire my mind to stop recognizing it as "unused variable." 4. I did the "design space analysis" [from above](https://bugs.ruby-lang.org/issues/18980#note-20) at feature introduction, and I still believe that while `_1` looks weird(ish) for those not used to it, it is a reasonable choice. At least in my book, it is arguably better than `@1` (associates with non-local name), `it` (looks like a "regular" name, not a distinguished special thing), or `_` (this one is _really_ used as an "unused argument" regularly). So... yeah. ---------------------------------------- Feature #18980: Re-reconsider numbered parameters: `it` as a default block parameter https://bugs.ruby-lang.org/issues/18980#change-99018 * Author: k0kubun (Takashi Kokubun) * Status: Open * Priority: Normal ---------------------------------------- ## Problem Numbered parameters (`_1`, `_2`, ...) look like unused local variables and I don't feel motivated to use them, even though I need this feature very often and always come up with `_1`. ```rb [1, 2, 3].each { puts _1 } ``` I have barely used it in the last 2~3 years because it looks like a compromised syntax. I even hesitate to use it on IRB. ### Why I don't use `_1` I'm not clever enough to remember the order of parameters. Therefore, when a block has multiple parameters, I'd always want to name those parameters because which is `_1` or `_2` is not immediately obvious. Thus I would use this feature only when a block takes a single argument, which is actually pretty common. If I use `_1`, it feels like there might be a second argument, and you might waste time to think about `_2`, even if `_2` doesn't exist, which is a cognitive overhead. If you use `it`, it kinda implies there's only a single argument, so you don't need to spend time remembering whether `_2` exists or not. It is important for me that there's no number in `it`. ## Proposal Hoping to introduce `it` as an alternative to `_1` later, experiment with warning `#it` method calls without any arguments or blocks. If nobody sees serious problems after some warning period, we'll implement `it` as follows: ### Specification ```rb [1, 2, 3].each { puts it } ``` `it`s behavior should be as close to `_1` as possible. `it` should treat array arguments in the same way as `_1`. `it` doesn't work in a block when an ordinary parameter is defined. `it` is implemented as a special case of `getlocal` insn, not a method. `it` without an argument is considered `_1` or a normal local variable if defined. `it` is considered a method call only when it has any positional/keyword/block arguments. ## Past discussions * [Feature #4475] default variable name for parameter: Proposed `it`, and merged as `@1`. * 2019/03/13: [DevelopersMeeting20190311Japan](https://docs.google.com/document/d/e/2PACX-1vTUCmj7aUdnMAdunG0AZo0AdWK-9jvfXcB7DWYmzGtmPc0IuIPGn7eLARoR5tBd6XUUB08W-hH74k-T/pub) * 2019/04/17: [DevelopersMeeting20190417Japan](https://docs.google.com/document/d/1hw6Xca8arG6b0V63zvWnNEtxIjEjEVzS10KXGhzZpI8/pub) * 2019/04/20: [Ruby Committers vs the World](https://youtu.be/5eAXAUTtNYU?t=3118) * [Feature #15723] Reconsider numbered parameters: Renamed `@1` to `_1`. * 2019/08/29: [DevelopersMeeting20190829Japan](https://docs.google.com/document/d/1XypDO1crRV9uNg1_ajxkljVdN8Vdyl5hnz462bDQw34/edit?usp=sharing) * [Feature #15897] `it` as a default block parameter: Proposed `it`, and got closed because `_1` was merged. ### Compatibility `it` has not necessarily been rejected by Matz; he just said [it's difficult to keep compatibility](https://bugs.ruby-lang.org/issues/4475#note-6) and [`it` or `this` _could_ break existing code](https://bugs.ruby-lang.org/issues/15723#note-2). It feels like everybody thinks `it` is the most beautiful option but is not sure if `it` breaks compatibility. But, in reality, does `it`? The following cases have been discussed: * `it` method, most famously in RSpec: You almost always pass a positional and/or block argument to RSpec's `it`, so the conflict is avoided with my proposal. You virtually never use a completely naked `it` ([comment](https://bugs.ruby-lang.org/issues/15897#note-29)). * `it` local variable: With the specification in my proposal, the existing code can continue to work if we consider `it` as a local variable when defined. With the specification in my proposal, existing code seems to break if and only if you call a method `#it` without an argument. But it seems pretty rare (reminder: a block given to an RSpec test case is also an argument). It almost feels like people are too afraid of compatibility problems that barely exist or have not really thought about options to address them. Also, you could always experiment with just showing warnings, which doesn't break any compatibility. Even if it takes 2~3 years of a warning period, I'd be happy to use that in 3 years. ### Confusion We should separately discuss incompatible cases and "works but confusing" cases. Potential confusion points: * RSpec's `it "tests something" do ... end` vs `it` inside the `do ... end` * `it` could be a local variable or `_1`, depending on the situation My two cents: You'd rarely need to write `it` directly under RSpec's `it` block, and you would just name a block argument for that case. In a nested block under a test case, I don't think you'd feel `it` is RSpec's. When you use a local variable `it = 1`, you'd use the local variable in a very small scope or few lines because otherwise, it'd be very hard to figure out what the local variable has anyway. So you'd likely see the assignment `it = 1` near the use of the local variable and you could easily notice `it` is not `_1`. If not, such code would be confusing and fragile even without this feature. The same applies when `it` is a method/block argument. I believe it wouldn't be as confusing as some people think, and you can always choose to not use `it` in places where `it` is confusing. -- https://bugs.ruby-lang.org/ Unsubscribe: