In Java, == is the strongest kind of equality (pointer equality): a == b always implies a.equals(b). However, in Ruby, == is weaker than .equals?:
ruby-1.9.2-rc2 > 17 == 17.0 => true ruby-1.9.2-rc2 > 17.equal?(17.0) => false So, where can I learn more about ==? What kind of checks should I expect when I compare two objects with it?
briefly this is what you need to know:
The == comparison checks whether two values are equal
eql? checks if two values are equal and of the same type
equal? checks if two things are one and the same object.
A good blog about this is here.
eq, eql, equal, equalp, and =. There are better named operators like string-equal and tree-equal though.
== to compare two objects? But even 5 is an object in Ruby... so what is it safe to use == to compare? Strings and numbers, certainly. What about arrays? Hashes?in reality they're both just methods == means object.==(other_object) equals? means object.equals?(other_object)
In this case, though, equals is used basically for hash lookup comparison i.e. a_hash[1] should not be the same key value pair as a_hash[1.0]
HTH. -r
== is, simply, a method. I think it is explained really well here:
Typically, this method is overridden in descendent classes to provide class-specific meaning.
along with an example with Numerics.
There's a pitfall here, though: as == is a method of the left operand, it is not always safe to assume that the result of a==b should be the same as of b==a. Especially in cases when a is a method call, which, in a dynamic language such as Ruby, must not always return values of the same type.
jruby-1.5.0 > 17 ==17 => true jruby-1.5.0 > 17 == 17.0 => true jruby-1.5.0 > 17 === 17.0 => true jruby-1.5.0 > 17.equal?(17.0) => false jruby-1.5.0 > 17.id => 35 jruby-1.5.0 > (17.0).id (irb):12 warning: Object#id will be deprecated; use Object#object_id => 2114 Everything in ruby is an object. the object 17 is not the same object as 17.0 and equal? compares objects, not values of objects.
