Issue #11618 has been reported by Kaneko Yuichiro.

----------------------------------------
Bug #11618: Safe call syntax with aref or aset is 
https://bugs.ruby-lang.org/issues/11618

* Author: Kaneko Yuichiro
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.3.0dev (2015-10-24 trunk 52128)
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
----------------------------------------
This test pass

```ruby
# ruby -v: ruby 2.3.0dev (2015-10-24 trunk 52128) [x86_64-darwin14]
# test/ruby/test_call.rb

  def test_safe_call_aref_aset
    s = Struct.new(:x, :y)
    o = s.new({a: 10})

    assert_equal(10, o.x.?send(:[], :a))
    o.x.?send(:[]=, :a, 11)
    assert_equal(11, o.x.?send(:[], :a))

    assert_nil(o.y.?send(:[], :a))
    o.y.?send(:[]=, :a, 11)
    assert_nil(o.y.?send(:[], :a))
  end
```

This is invalid syntax

```ruby
# ruby -v: ruby 2.3.0dev (2015-10-24 trunk 52128) [x86_64-darwin14]
# test/ruby/test_call.rb

  def test_safe_call_aref_aset
    s = Struct.new(:x, :y)
    o = s.new({a: 10})

    assert_equal(10, o.x.?[:a])
    o.x.?[:a] = 11
    assert_equal(11, o.x.?[:a])

    assert_nil(o.y.?[:a])
    o.y.?[:a] = 11
    assert_nil(o.y.?[:a])
 end
```

```
./test/runner.rb: ruby/ruby/test/ruby/test_call.rb:60: syntax error, unexpected '[', expecting '(' (SyntaxError)
    assert_equal(10, o.x.?[:a])
                           ^
ruby/ruby/test/ruby/test_call.rb:61: syntax error, unexpected '[', expecting '('
    o.x.?[:a] = 11
          ^
ruby/ruby/test/ruby/test_call.rb:62: syntax error, unexpected '[', expecting '('
    assert_equal(11, o.x.?[:a])
                           ^
ruby/ruby/test/ruby/test_call.rb:64: syntax error, unexpected '[', expecting '('
    assert_nil(o.y.?[:a])
                     ^
ruby/ruby/test/ruby/test_call.rb:65: syntax error, unexpected '[', expecting '('
    o.y.?[:a] = 11
          ^
ruby/ruby/test/ruby/test_call.rb:66: syntax error, unexpected '[', expecting '('
    assert_nil(o.y.?[:a])
                     ^
make: *** [yes-test-all] Error 1
```



-- 
https://bugs.ruby-lang.org/