From: Dave Thomas <Dave@...>
Date: 2001-11-28T23:48:00+09:00
Subject: [ruby-talk:26803] Re: String#== : Why not error with different type?

furufuru@ccsr.u-tokyo.ac.jp (Ryo Furue) writes:

> I've considered the problem hard and I think I understand.  I think
> the earlier example Matz gave
> 
>  	ary.select{|x| x == "foo"}
> 
> is an answer.  This does have a danger, which I described earlier. 
> But, design 1 would complicate this much, as he said.  And this
> (perhaps) outweighs the danger.  So I'm (perhaps :) convinced.

Think of this in human terms. If I point at a cow, and ask you "is
this a car?", do you do the Star Trek thing, screaming "this does not
compute, this does not compute" until your head explodes? Or do you
look at me calmly, say "no", and wonder if perhaps my medication is
wearing off.

It's the same with Ruby.

   if a_cow == a_car
     puts "act surprised"
   end

Remember, in Ruby, classes aren't types, so it would be pretty hard to
implement equality which used type checks.

> Finally, I'd like to find a way to avoid the danger.  Could someone
> tell me what "the unit test" is?  Is it RubyUnit?  Where can I find a
> documentation?  I searched the Ruby-talk archive, but there too many
> articles that mention RubyUnit...

Unit testing is a philosophy of testing your code in small chunks,
normally writing tests as you go along. You use unit tests to
investigate and verify the internal behavior of code, while you'd use
functional or acceptance tests to investigate the code's overall
behavior. Typically you'd write one or more tests for each non-trivial
method that you write. For example, here's some lines from the unit
test for a routine that (among other things) expands tabs:

  def test_tabs
    str = "hello\n  dave"
    assert_equal(str, basic_conv(str))
    str = "hello\n\tdave"
    assert_equal("hello\n        dave", basic_conv(str))
    str = "hello\n \tdave"
    assert_equal("hello\n        dave", basic_conv(str))

To make writing unit tests easier, you can use a framework. Runy has
two good frameworks, RubyUnit and Lapidary. The code above uses the
assert_ methods of RubyUnit.


Dave