From: 7stud -- <bbxx789_05ss@...>
Date: 2008-03-04T18:10:59+09:00
Subject: Re: and statement

unknown wrote:
> Hi,
> 
> I found the following statement in routing.rb of rails framework. I
> haven't seen this kind of usage anywhere. Can somebody tell me what
> does this statement do? I am particularly interested in knowing how
> 'and' behaves here.
> 
> result = route.recognize(path, environment) and return result
> 

result = true and true
puts result

result =  false and false
puts result

puts

x = 10
result = false and x = 20
puts result
puts x

result = true and x = 20
puts result
puts x

--output:--
true
false

false
10
true
20


The results are due to 'short circuiting' of the conditionals.  If you 
have this statement:

x and y

and x is false, then there is no way for the whole conditional to 
evaluate to true.  As a result, there is no need to evaluate the second 
expression y to determine the result of the conditional--its going to be 
false no matter what y evaluates to, and ruby chooses not to evaluate y.

The statement:

result = route.recognize(path, environment) and return result

is equivalent to:

result = route.recognize(path, environment)
if result
  return result
end
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