From: "D. Deryl Downey" <me@...>
Date: 2013-03-04T06:24:55+09:00
Subject: Re: Confusion with Ruby's "case/when" block statement

As *clearly* stated (even within ANY ruby language tutorial explaining how
ruby works)

"A case expression searches for a match by starting at the first (top
left) comparison, performing comparison === target. When a comparison
returns true, the search stops, and the body associated with the
comparison is executed. case then returns the value of the last expression
executed. If no comparison matches: if an else clause is present, its body
will be executed; otherwise, case silently returns nil."

There's the 'test' it performs, AND what method is run *for* the test, AND
what happens afterwards.

READ IT!


On 3/3/13 3:50 PM, "Kumar R." <lists@ruby-forum.com> wrote:

>Ruby uses `===` operator on the `case/when` type execution style.Now It
>also known that Ruby depending on the type
>of the thing present in the `when` clause, calls the respective `.===`
>method.
>
>Say `when` statement contains the `class` names, then the rule is - ` it
>will use Module#===, which will return true if the right side is an
>instance of,
>or subclass of, the left side.` One example with this context is:
>
>Here `instance of` test occurs
>
>obj = 'hello'
>#=> "hello"
>case obj
>when String
>print 'It is a string'
>when Fixnum
>print 'It is a number'
>else
>print 'It is not a string'
>end
>#It is a string
>#=> nil
>
>Here `subclass of` test occurs
>
>num = 10
>#=> 10
>case num
>when Numeric
>puts "Right class"
>else
>puts "Wrong class"
>end
>#Right class
>#=> nil
>
>Now `when` contains `String` literals then String#=== is called, which
>in turn checks if left and right handside
>literal are same(same chracter in same sequence) or not.
>
>a = "abc"
>#=> "abc"
>case a
>when "def" then p "Hi"
>when "abc" then p "found"
>else "not found"
>end
>#"found"
>#=> "found"
>
>The all logic is too cool. Now my query is with `case/when` structure -
>
>How does ruby know if `when` holding `class`, or `String` literals or
>anything valid at runtime?
>
>or
>
>What test does it perform before calling the respective `.===` operator.
>
>-- 
>Posted via http://www.ruby-forum.com/.
>