===.() not being called in case statement

Rails
1

I’ve been trying to get the open_id_authentication plugin to play nice
in my applications, and after a few hours of trial and error I have it
running. I had to make a number of changes from the README text, and
I’m trying to pin down what is going on with the case statement for
status. Here is a simplified version that still exhibits the problem:

class Result
def self.
new(code)
end

def initialize(code)
@code = code
end

def ===(code)
puts ‘===’
@code == code
end
end

result = Result[:successful]

case result
when :successful
puts ‘successful’
else
puts ‘unsuccessful’
end

My expected output:

successful

But the actual output is:
unsuccessful

My understanding is that case statements use the === function for
comparisons. And in some cases they certainly do (I have seen it work
on other examples). It would appear that in this case the === is not
even being called at all (I tried to pin down what function was being
called, but didn’t have much luck).

Could somebody please explain to me why this doesn’t work or how one
might fix it?

2

monki wrote:

new(code)

end

on other examples). It would appear that in this case the === is not
even being called at all (I tried to pin down what function was being
called, but didn’t have much luck).

Could somebody please explain to me why this doesn’t work or how one
might fix it?

The === function is called on the object in the when condition, with
the case object as the parameter, not the other way around. It won’t
work with the simplified code you’ve presented, but you’ll probably
have to write something like:

result = Result[:successful]

case result
when Result[:successful] then puts ‘successful’
else puts ‘unsuccessful’
end

–
We develop, watch us RoR, in numbers too big to ignore.

3

The === function is called on the object in the when condition, with
the case object as the parameter, not the other way around. It won’t
work with the simplified code you’ve presented, but you’ll probably
have to write something like:
That would certainly explain some things, and why it works in the
examples I had seen.

result = Result[:successful]

case result
when Result[:successful] then puts ‘successful’
else puts ‘unsuccessful’
end
I figured it could be done this way, but it seemed wasteful to create
a new object instance just to compare against.

Not exactly sure what I want to do with it at present, but this
definately makes it much clearer what is going on.

Thanks for the insight.

4

monki wrote:

My understanding is that case statements use the === function for
comparisons. And in some cases they certainly do (I have seen it work
on other examples). It would appear that in this case the === is not
even being called at all (I tried to pin down what function was being
called, but didn’t have much luck).

Could somebody please explain to me why this doesn’t work or how one
might fix it?

Can’t do it for the reasons listed above but this looks almost as
pretty
irb(main):002:0> class Result
irb(main):003:1> def self.
irb(main):004:2> new(code)
irb(main):005:2> end
irb(main):006:1> def initialize(code)
irb(main):007:2> @code = code
irb(main):008:2> end
irb(main):009:1> def to_sym
irb(main):010:2> @code
irb(main):011:2> end
irb(main):012:1> end
=> nil
irb(main):013:0> result = Result[:successfull]
=> #<Result:0x360a88 @code=:successfull>
irb(main):014:0> case result.to_sym
irb(main):015:1> when :successfull
irb(main):016:1> puts ‘yay’
irb(main):017:1> else
irb(main):018:1* puts ‘nay’
irb(main):019:1> end
yay
=> nil

5

In the end I think it makes the most sense to just add an attr_reader,
and do away with the non-working === (even though it would be nice to
handle the comparison automagically)

class Result
attr_reader :code

def self.
new(code)
end

def initialize(code)
@code = code
end
end

result = Result[:successful]

case result.code
when :successful
puts ‘successful’
else
puts ‘unsuccessful’
end

Which, as one might expect, gives you:
successful

In any event it is quite good to know the order of operations for
case. I couldn’t find anything that described the order and it makes
a big difference when you are comparing objects of different classes.