From: shugo@...
Date: 2015-12-17T13:33:00+00:00
Subject: [ruby-core:72214] [Ruby trunk - Bug #11816] Partial safe navigation	operator

Issue #11816 has been updated by Shugo Maeda.


Yusuke Endoh wrote:
> > Is it really hard to change after the release of Ruby 2.3?
> 
> As Marc-Andre stated in https://bugs.ruby-lang.org/issues/11816#note-7, it will bring incompatibility.  If we may change the spec in future, I think we should explicitly state the possibility in doc and release message.  Also, it might be a good idea to mark the feature as "experimental".

It would be better if Matz would like to change the behavior in future.

> Another idea for the proposal: how about propagating `&.` as long as explicit method chain (that uses `.` literally) continues?
> 
> ~~~~
> x&.foo * 42   ==  (x&.foo) * 42
> x&.foo.*(42)  ==  (x&.foo&.*(42))  # strictly not equivalent in the case where #foo returns nil
> ~~~~

In my understanding, rather than `(x&.foo&.*(42))`, `x&.foo.*(42)` is equivalent to `x && x.foo.*(42)` except when `x` is `false`.
So, the phrase "propagating `&.`" is confusing, isn't it?

Anyway, your proposal sounds reasonable because `x&.foo * 42` is parsed as `(x && x.foo) * 42` rather than `x && (x.foo * 42)` in my brain.
However, the behavior like `(x && x.foo) * 42` seems to be useless for the same reason as the current behavior of `x&.foo.bar`, so there is a trade-off.


----------------------------------------
Bug #11816: Partial safe navigation operator
https://bugs.ruby-lang.org/issues/11816#change-55624

* Author: Marc-Andre Lafortune
* Status: Open
* Priority: Normal
* Assignee: Yukihiro Matsumoto
* ruby -v: preview 2
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
----------------------------------------
I'm extremely surprised (and disappointed) that, currently:

    x = nil
    x&.foo.bar # => NoMethodError: undefined method `bar' for nil:NilClass

To make it safe, you have to write `x&.foo&.bar`. But if `foo` is never supposed to return `nil`, then that code isn't "fail early" in case it actually does. `nil&.foo.bar` is more expressive, simpler and is perfect if you want to an error if `foo` returned `nil`. To actually get what you want, you have to resort using the old form `x && x.foo.bar`...

In CoffeeScript, you can write `x()?.foo.bar` and it will work well, since it gets compiled to

    if ((_ref = x()) != null) {
      _ref.foo.bar;
    }

All the discussion in #11537 focuses on `x&.foo&.bar`, so I have to ask:

Matz, what is your understanding of `x&.foo.bar`?

I feel the current implementation is not useful and should be changed to what I had in mind. I can't see any legitimate use of `x&.foo.bar` currently.




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