From: shugo@...
Date: 2015-12-18T04:06:08+00:00
Subject: [ruby-core:72258] [Ruby trunk - Bug #11816] Partial safe navigation	operator

Issue #11816 has been updated by Shugo Maeda.


Shugo Maeda wrote:
> 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.

Just for clarification, `x&.foo.bar` as `(x && x.foo).bar` looks more natural to me than `x && x.foo.bar`.

> 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.

So there is also a trade-off between the current behavior and Endoh-san's proposal.



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Bug #11816: Partial safe navigation operator
https://bugs.ruby-lang.org/issues/11816#change-55645

* 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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