Ruby: Case using object

FWIW, you don't need to pass an object to a case statement in 1.8.7 at all.

foo = Foo.new()casewhen foo.bar == this then thatwhen foo.baz == this then thatend

I was surprised as hegg.

http://www.skorks.com/2009/08/how-a-ruby-case-statement-works-and-what-you-can-do-with-it/

What case .. when does is it calls the method === on your when values, passing your foo object as the argument to the === method. So in this code:

case foowhen 1 then "something"when 2 then "something else"when 3 then "another thing"end

It will try 1 === foo, then 2 === foo, then 3 === foo, until one of them returns a truthy value.

One way of making case .. when more powerful is using Procs as the when values. I'm not sure about earlier versions of Ruby, but in 1.9, proc === x is equivalent to proc.call(x). So you can write code like this:

case foowhen Proc.new { foo.bar == 1 } then "something"when Proc.new { foo.bar == 2 } then "something else"when Proc.new { foo.baz == 3 } then "another thing"end

Note that we don't even have to pass foo into the Procs, since we already have access to it. I don't think this is a very good choice of control structure for this example, a simple chain of ifs would make more sense:

if foo.bar == 1  "something"elsif foo.bar == 2  "something else"elsif foo.baz == 3  "another thing"end

It looks like you're wanting to change the default receiver. This is hacky, but you could do something like:

string = Foo.new.instance_eval do  if bar==1 then "something"  elsif bar==2 then "something else"  elsif baz==3 then "another thing"  endend

That's a big, terrible code smell, though, if you're just doing it because you're lazy. If you're doing it because you're creating a DSL, that's something else.