From: Robert Klemme <shortcutter@...>
Date: 2009-10-27T17:35:31+09:00
Subject: Re: Array#collect in a method call, not working for me

Please do not top post.

2009/10/26 Michael Randall <randallsata@gmail.com>:
> OK, I *thought* that part was working, but now I see that it wasn't
> really. So to help me understand I wrote the following, to see what it
> does and I see that adding the #inspect will give me the string to
> compare against.
>
> But does that mean that (a = [1, 2].class) is setting a to be an Array?
> Oh, and thank you!
>
> Here is my test...
>
> irb(main):034:0* def proovy( n )
> irb(main):035:1>   a = n.class.inspect
> irb(main):036:1>   b = n.class
> irb(main):037:1>   puts "a: #{a}"
> irb(main):038:1>   puts "b: #{b}"
> irb(main):039:1>   case a
> irb(main):040:2>     when "Array"  : puts "a matched Array in case"
> irb(main):041:2>     when "Fixnum" : puts "a matched Fixnum in case"
> irb(main):042:2>   end
> irb(main):043:1>   case b
> irb(main):044:2>     when "Array"  : puts "b matched Array in case"
> irb(main):045:2>     when "Fixnum" : puts "b matched Fixnum in case"
> irb(main):046:2>   end
> irb(main):047:1> end

Note that you can simplify the test:

irb(main):004:0> [[], "foo"].each {|obj| case obj
irb(main):005:2> when Array
irb(main):006:2> printf "%p is an array\n", obj
irb(main):007:2> when String
irb(main):008:2> printf "%p is a string\n", obj
irb(main):009:2> else
irb(main):010:2* printf "i don't know what %p is.\n", obj
irb(main):011:2> end}
[] is an array
"foo" is a string
=> [[], "foo"]

case uses the === operator:

irb(main):012:0> Array === [1,2,3]
=> true
irb(main):013:0> Array === "foo"
=> false
irb(main):014:0> String === "foo"
=> true

IMHO testing against the class is superior to testing against the
type's name.  Here's why: in case of inheritance the name test will
fail while the class test still succeeds

irb(main):016:0> class FooArray < Array; end
=> nil
irb(main):017:0> Array === FooArray.new
=> true
irb(main):018:0> "Array" === FooArray.name
=> false

Kind regards

robert

-- 
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