Need help regarding conditionals on while loops

Ruby
1

In a tutorial I’m currently reading
(http://pine.fm/LearnToProgram/?Chapter=10), this came up.

def doUntilFalse firstInput, someProc
input = firstInput
output = firstInput

while output
input = output
output = someProc.call input
end

input
end

They never really explained how this works though:

while output

What exactly is Ruby checking for here? The author uses this code for
the method:

puts doUntilFalse([5], buildArrayOfSquares).inspect

So the while loop would be something like this: “while [5]”
Shouldn’t it be like “while [5] != something”?

I’m extremely confused about this :), as far as I can see, it’s like
asking ‘What’s the difference between an elephant.’ If someone could
just simply explain this it would be awesome! Thanks in advance!

2

On Sep 13, 2011, at 10:49 PM, Kane W. wrote:

They never really explained how this works though:

while output

The while loop body is executed if the expression evaluates to a
true-ish value.
In this case the expression is simply the local variable ‘output’.

In Ruby all values are considered true except for nil and false. In
particular
0 is considered true as is an empty string, empty array, and empty hash
("", [], {}).
This often trips up Ruby newcomers.

So in your example

end
the while loop will continue iterating until someProc returns a
false-ish value
(either nil or false). The output of someProc is reused as its input for
the
next iteration.

Gary W.

3

Thanks that was very helpful!