[ruby-core:82237] [Ruby trunk Bug#13781] Should the safe navigation operator invoke `nil?`

Issue #13781 has been updated by marcandre (Marc-Andre Lafortune).


Short answer is "no".

Longer answer is:
- is there an actual use case? I very much doubt there is one
- BasicObject does not respond to `nil?`, so the safe operator would not work in that case?
- other Ruby conditional (like `if foo` or `foo ? bar : baz`) do not call `nil?` or `==(nil)`, they simply do a straight comparison with `nil` and `false`. That's the way it should be for the safe navigation operator too.

----------------------------------------
Bug #13781: Should the safe navigation operator invoke `nil?`
https://bugs.ruby-lang.org/issues/13781#change-66017

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 2.4.1
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
----------------------------------------
In the following example:

~~~
class Later < BasicObject
	def initialize(&block)
		raise ::ArgumentError, "Block required" unless block
		
		if block.arity > 0
			raise ::ArgumentError, "Cannot store a promise that requires an argument"
		end
		@block  = block
	end
	
	def __resolve__
		@result ||= @block.call
	end
	
	def nil?
		__resolve__.nil?
	end
	
	def respond_to?(name)
	  __resolve__.respond_to?(name)
	end
	
	def method_missing(name, *args, &block)
		__resolve__.__send__(name, *args, &block)
	end
end

Person = Struct.new(:name, :age)

person = Later.new do
  nil # Person.new("Froob", 200)
end

puts person.nil?
puts person&.name
~~~

The code fails because person is a proxy object.

If safe navigation operator invoked `nil?` it should work. But, it's not clear exactly how the implementation should behave, or whether it's possible to implement this style of proxy.



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