[ruby-core:105263] [Ruby master Feature#14579] Hash value omission

Issue #14579 has been updated by shugo (Shugo Maeda).


duerst (Martin D=FCrst) wrote in #note-25:
> Ah, so `{if:}` means something close to `{if: local_variable_get(:if)}` a=
nd '{self:}` means something close to `{self: local_variable_get(:self)}` (=
and NOT `{self: self}`). =


Yes.
Technically speaking, `send(:if)` is used instead of local_variable_get if =
the local variable is not defined.

> Not sure we need this, but also not sure it hurts.

In the meeting just after RubyKaigi, someone pointed out that `{if:}[:if]` =
is faster than `binding.local_variable_get(:if)`.

```
excelsior:ruby$ cat bm.rb
require "benchmark"

Benchmark.bmbm do |b|
  ->(if:) {
    b.report("binding.local_variable_get") do
      10000.times do
        binding.local_variable_get(:if)
      end
    end
    b.report("new hash syntax") do
      10000.times do
        {if:}[:if]
      end
    end
  }.call(if: 123)
end
excelsior:ruby$ ./ruby bm.rb
Rehearsal --------------------------------------------------------------
binding.local_variable_get   0.005680   0.000211   0.005891 (  0.005889)
new hash syntax              0.001817   0.000136   0.001953 (  0.001965)
----------------------------------------------------- total: 0.007844sec

                                 user     system      total        real
binding.local_variable_get   0.003668   0.000094   0.003762 (  0.003763)
new hash syntax              0.000829   0.000162   0.000991 (  0.001042)
```


----------------------------------------
Feature #14579: Hash value omission
https://bugs.ruby-lang.org/issues/14579#change-93673

* Author: shugo (Shugo Maeda)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
----------------------------------------
How about to allow value omission in Hash literals:

```ruby
x =3D 1
y =3D 2
h =3D {x:, y:}
p h #=3D> {:x=3D>1, :y=3D>2}
```

And in keyword arguments:

```ruby
def login(username: ENV["USER"], password:)
  p(username:, password:)
end

login(password: "xxx") #=3D> {:username=3D>"shugo", :password=3D>"xxx"}
```


---Files--------------------------------
hash_value_omission.diff (619 Bytes)


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