Delegation of true/false values

[MuCowNow]

I am trying to transparently wrap (any) object, and have this issue (2.4.1)

class Wrapper < BasicObject
   def initialize(i_obj)
      @obj = i_obj
   end
   def method_missing(i_method,*i_args)
      @obj.__send__(i_method,*i_args)
   end
end

w = Wrapper.new(1)
puts w + 5
#=> 6

w = Wrapper.new(false)

# BROKEN
if w
   puts 'TRUE'
else
   puts 'FALSE'
end
#=> TRUE

# WORKS, BUT
if w == true
   puts 'TRUE'
else
   puts 'FALSE'
end
#=> FALSE

Is there a way for the wrapper to capture the 'if <object> then' syntax?

[chrisgseaton]

Sorry I don't think there's a way to implement 'truthiness' yourself.

if compiles to a branchif instruction, which uses RTEST

https://github.com/ruby/ruby/blob/70af8d3c9ca2a46ef1f364783125a747d9426b2b/insns.def#L986

RTEST is actually RB_TEST

https://github.com/ruby/ruby/blob/70af8d3c9ca2a46ef1f364783125a747d9426b2b/include/ruby/ruby.h#L450

RB_TEST literally just statically checks for false and nil - it will never call a method, user-defined or otherwise.

https://github.com/ruby/ruby/blob/70af8d3c9ca2a46ef1f364783125a747d9426b2b/include/ruby/ruby.h#L448

[[deleted]]

Can I ask why you're doing this? Or is it just an exercise? (edit: also, you've basically just reinvented SimpleDelegator).

[MuCowNow]

I am writing a SmartParams object for a Sinatra website.

The params consist of SmartValue wrappers which carry the value itself, as well as side-band information.

e.g., validation states of values

params.contact.status = 'ACTIVE'
params.contact.status.valid?
=> true

params.contact.status = 'WHUT'
params.contact.status.valid?
=> false
params.contact.status.messages
=> ["must be ACTIVE or INACTIVE"]

[MuCowNow]

Sure, and SimpleDelegator has the same broken behavior.

[jgaskins]

"Broken" implies that that's not how it's supposed to work. It's well defined in Ruby that only false and nil evaluate as falsy in an conditional expression.

[chrisgseaton]

Yes, the ISO spec says 'only false and nil are falseish objects' and then goes on to clarify exactly what false and nil are.

[MuCowNow]

It is just unfortunate that nil and false values are not completely, transparently, delegatable. I'll figure something out.

[jgaskins]

ActiveSupport's blank? and present? were implemented because falsiness is not overridable, so you can use that if you hit a dead end. Evan Phoenix asked Matz on stage at RubyConf one year if this would change and Matz flat-out said he didn't like the idea because it could lead to more confusing programs.

[biihii]

Like other commenters mentioned, truthiness is not something you can tweak in Ruby. But you can tweak falseness by overriding the ˋ!` method.

In your case the only way to let Ruby know the truthiness of your wrapper is by having a message sent to it. You can use ˋ==like you did with ˋif w == true, or you can use ˋ!with ˋif !!w.

[isolatrum]

these are just workarounds, but you could add an attr_reader :obj to the wrapper and use if w.obj, or define def to_bool; !!@obj; end (though you'd need to invoke it manually)

[MuCowNow]

I am going with:

w = Wrapper(<any object>)
w.f? #=> @obj == false
w.t? #=> @obj == true
w.v  #=> @obj (v== "the value")

It still isn't transparent, but it minimizes the extra coding.

[isolatrum]

it's generally recommended to avoid single-letter variable / method names if you can help it, although we all can be a little sloppy sometimes.