From: matt.larraz@...
Date: 2015-12-16T00:38:20+00:00
Subject: [ruby-core:72165] [Ruby trunk - Bug #11816] Partial safe navigation	operator

Issue #11816 has been updated by Matt Larraz.


My na��ve understanding is that `foo&.bar` should be a shorthand for `foo && foo.bar`, and therefore the `&.` operator should take the same level of precedence as the `&&` operator.

Marc-Andre Lafortune wrote:
>     x = nil
>     x&.foo.bar # => nil
>     x&.foo[42] # => nil
>     x&.foo[42] = 43 # => nil
>     x&.foo * 42 # => nil 
>     x&.foo + 42 # => nil
>     x&.foo << 42 # => nil
>     x&.foo < 42 # => nil
>     x&.foo == 42 # => false     ### This is where the precedence of &. is higher
>     x&.foo || 42 # => 42
>     x&.foo ? 1 : 2  # => 2

If you substitute `x&.foo` for `x && x.foo` in the above, they all evaluate the same except for one:

~~~
x && x.foo == 42 # => nil
~~~
This makes sense, since `==` is a method and not an operator.

----------------------------------------
Bug #11816: Partial safe navigation operator
https://bugs.ruby-lang.org/issues/11816#change-55576

* 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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