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List:       ruby-core
Subject:    [ruby-core:86773] [Ruby trunk Bug#14719] FalseClass wrapping a SimpleDelegator evaluates to true in 
From:       declan () weuseopensource ! com
Date:       2018-04-30 9:05:51
Message-ID: redmine.journal-71728.20180430090550.f97bcd0462be4bbf () ruby-lang ! org
[Download RAW message or body]

Issue #14719 has been updated by theirishpenguin (Declan McGrath).


Thanks Marc-Andre. Appreciate the quick response.

----------------------------------------
Bug #14719: FalseClass wrapping a SimpleDelegator evaluates to true in an IF \
statement https://bugs.ruby-lang.org/issues/14719#change-71728

* Author: theirishpenguin (Declan McGrath)
* Status: Rejected
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-linux]
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
Hi, thanks for Ruby :-)

I have run into a problem. When I wrap the boolean false in a SimpleDelegator it \
breaks the semantics of the boolean when evaluated in expressions such as IF \
statements - returning true when I would have expected false.

Here is a test case...

~~~ ruby
class BoldBool < SimpleDelegator                                                      \
 end                                                                                  \
                
                                                                                      \
 false_bool = BoldBool.new(false)                                                     \
                
                                                                                      \
 if false_bool                                                                        \
  puts "I'm evaluated as true but I should be false."                                 \
 end 
~~~

When I run it I get:
#=>I'm evaluated as true but I should be false.

Expected result:
No output.

I understand that there may be good reasons for why this is happening (eg. the class \
of the object false_bool may be a BoldBool and this is not a FalseClass) however it \
breaks the fundamental semantics of a boolean - in which case I think we should \
consider raising an ArgumentError in the Ruby language if a Boolean is passed to the \
constructor of a SimpleDelegator.

I tried to workaround the problem by overriding equals?(). I am guessing that this \
would be the correct approach - and that this is what is used by the IF expression to \
determine whether it is dealing with a truthy object or a falsey...

~~~ ruby
class BoldBool < SimpleDelegator                                                      \
  def equal?(obj)                                                                     \
                
        if __getobj__.is_a? FalseClass and obj == false                               \
                
            return true                                                               \
                
        else                                                                          \
                
            __getobj__.equal?(obj)                                                    \
                
        end                                                                           \
  end                                                                                 \
 end                                                                                  \
                
                                                                                      \
 false_bool = BoldBool.new(false)                                                     \
                
                                                                                      \
 if false_bool                                                                        \
  puts "I'm evaluated as true but I should be false."                                 \
 end
~~~

However this gives me the error...

~~~ ruby
/home/me/.rvm/rubies/ruby-2.4.1/lib/ruby/2.4.0/delegate.rb:313:in `__getobj__': not \
                delegated (ArgumentError)
        from simple_delegator_on_boolean_with_equals_override.rb:5:in `equal?'
        from /home/me/.rvm/rubies/ruby-2.4.1/lib/ruby/2.4.0/delegate.rb:333:in \
                `__setobj__'
        from /home/me/.rvm/rubies/ruby-2.4.1/lib/ruby/2.4.0/delegate.rb:72:in \
                `initialize'
        from simple_delegator_on_boolean_with_equals_override.rb:13:in `new'
        from simple_delegator_on_boolean_with_equals_override.rb:13:in `<main>'
~~~

If I try an even simpler override approach as an experiment this errors too...

~~~ ruby
class BoldBool < SimpleDelegator                                                      \
  def equal?(obj)                                                                     \
                
        true                                                                          \
  end                                                                                 \
 end                                                                                  \
                
                                                                                      \
 false_bool = BoldBool.new(false)                                                     \
                
                                                                                      \
 if false_bool                                                                        \
  puts "I'm evaluated as true but I should be false."                                 \
 end      
~~~

... with the error...

~~~ ruby
/home/me/.rvm/rubies/ruby-2.4.1/lib/ruby/2.4.0/delegate.rb:333:in `__setobj__': \
                cannot delegate to self (ArgumentError)
        from /home/me/.rvm/rubies/ruby-2.4.1/lib/ruby/2.4.0/delegate.rb:72:in \
                `initialize'
        from simple_delegator_on_boolean_with_simple_equals_override.rb:9:in `new'
        from simple_delegator_on_boolean_with_simple_equals_override.rb:9:in `<main>'
~~~

Is this SimpleDelegator behaviour a bug? (downloadable files attached containing the \
above snippets).

---Files--------------------------------
simple_delegator_on_boolean.rb (167 Bytes)
simple_delegator_on_boolean_with_equals_override.rb (335 Bytes)
simple_delegator_on_boolean_with_simple_equals_override.rb (208 Bytes)


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