From: Piergiuliano Bossi <p_bossi_AGAINST_SPAM@...>
Date: 2004-03-05T01:49:50+09:00
Subject: Re: Ruby won, of course

Robert Klemme wrote:
>>You are right, my fault. Fact is that having eliminated combine_results
>>method I now combine values using '&&' (or 'and'), which in turn
>>performs a short-circuit evaluation ==> if the failing test is in the
>>first group combined through '&&' the second group will never be
> 
> evaluated.
> 
>>I start thinking that combine_results cannot be avoided...
> 
> 
> I'm afraid you're a bit confused now. :-)  What do you want
> combine_results for?  It does not make a difference, because you eval'ed t
> before.  And even if you didn't, switching order is sufficient.  You did
> (with the slight modification of pulling v=eval(t) out of the string):
> 
> def check(*tests)
>       stack = caller.map {|m| m[/\w*(?=')/]}.compact.reverse.join " "
>       tests.inject(true) {|ret, t| v=eval(t); puts "#{v ? 'pass' : 'FAIL'}
> .... (#{stack}) #{t.strip}"; ret && v}
> end
> 
> It doesn't matter whether "ret && v" short circuits or not, because you
> did eval it already.  And even if you didn't you could do "eval(t) && ret"
> which would always eval.

Ok, I have to repost the code, otherwise we don't understand each other.

****************CUT HERE****************
def check(*tests)
   stack = caller.map {|m| m[/\w*(?=')/]}.reverse.join(" ").strip
   tests.inject(true) {|ret, t| puts "#{(v=eval(t))?'pass':'FAIL'} ... 
(#{stack}) #{t}"; ret && v}
end

def test_plus
   check(
     "1 + 2 == 3",
     "1 + 2 + 3 == 6",
     "-1 + -3 == -4")
end
def test_multiply
   check(
     "2 * 2 == 4",
     "3 * 5 == 15")
end

def test_aritmetic
   test_plus &&
   test_multiply	
end

def test_math
   test_aritmetic
end

result = test_math
puts "result=#{result}"
****************CUT HERE****************

I'm talking of the '&&' inside test_aritmetic: using inject directly 
instead of combine_results makes executing the first group of test only.

Try to change first test from "1 + 2 == 3" to "1 + 1 == 3" ==> you will get:
****************CUT HERE****************
FAIL ... (test_math test_aritmetic test_plus) 1 + 1 == 3
pass ... (test_math test_aritmetic test_plus) 1 + 2 + 3 == 6
pass ... (test_math test_aritmetic test_plus) -1 + -3 == -4
result=false
****************CUT HERE****************

instead of

****************CUT HERE****************
FAIL ... (test_math test_aritmetic test_plus) 1 + 1 == 3
pass ... (test_math test_aritmetic test_plus) 1 + 2 + 3 == 6
pass ... (test_math test_aritmetic test_plus) -1 + -3 == -4
pass ... (test_math test_aritmetic test_multiply) 2 * 2 == 4
pass ... (test_math test_aritmetic test_multiply) 3 * 5 == 15
result=false
****************CUT HERE****************

The former is wrong.

In order to fix this I should use some form of inject in test_aritmetic 
too, creating a duplication that can be removed reintroducing 
combine_results only. That method was defined as:

****************CUT HERE****************
def combine_results(*tests)
   tests.inject {|t1, t2| t1 && t2}
end
****************CUT HERE****************

I hope that now it is clear. :-)

Ciao, Giuliano

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