Question

I need a class that can represent probabilities. It can be represented like a float between 0 and 1, and anything below 0.5 should evaluate to false. (or it can be between 1 and -1, anything negative is false)

p = A.probability() 
puts p # will output 0.3
if(p)
  puts 'success'
else
  puts 'failure'
end
# will outputs 'failure'

From this post it seems to suggest it is possible: every object has a boolean value… Most objects in Ruby will have a boolean value of true. Only two objects have a boolean value of false. Just that I need to set this boolean value somehow. So is this possible?

Answer 1

I wanted to do something similar, but unfortunately this is not possible in Ruby.

The only two objects that have a boolean value of false are false itself and nil. A few weeks ago I had a an internet chat (IRC) discussion with Brixen, one of the main developers of rubinius, and he explained it pretty well. My understanding is that when Ruby decides whether an object is true or not, it does NOT call any methods on (i.e. send any messages to) the object, it simply looks at the pointer it has to the object to see whether the pointer itself is equal to false or nil. Since it doesn’t call any methods on the object, there is no way for you to change the behavior.

The best you can do is something like this:

p = A.probability() 
puts p # => 0.3
if p.to_bool
  puts 'success'
else
  puts 'failure'
end