Binary Logic, Bug or Feature?

Ruby
1

Hi Guys,

I have been pulling my hair out for the last 20 minutes trying to find
out what is wrong in my app that has some pretty basic binary logic.
Here is a concise example in an irb session that shows my problem
(certainly, what I was working on wasn’t nearly as simple the sides of
AND were variables etc.):

?> x = true and true
=> true

x
=> true

(this is what I expect, true and true = true)

x = true and false
=> false

x
=> true

But what I’ve got here is “true and false” == false, but it assigns
true to x. So true and false == false, but really == true… Have I
lost my mind, should it do this? Does it do it for anyone else? It
seems weird to me since the first example does what I expect, but the
second doesn’t…

So now I’m reduced to doing something like:
if (true and false) then x = true else x = false end
which is kind of annoying, and not very ruby-esque IMO.

Any advice appreciated!

$ ruby -v
ruby 1.8.5 (2006-08-25) [i486-linux]

OS is Ubuntu 7.04.

(I know, old ruby ver - its just the stock ubuntu one)

THANKS!

  • Malcolm.
2

Hi,

In message “Re: Binary Logic, Bug or Feature?”
on Wed, 28 Nov 2007 13:33:36 +0900, “Malcolm L.”
[email protected] writes:

|I have been pulling my hair out for the last 20 minutes trying to find
|out what is wrong in my app that has some pretty basic binary logic.
|Here is a concise example in an irb session that shows my problem
|(certainly, what I was working on wasn’t nearly as simple the sides of
|AND were variables etc.):
|
|?> x = true and true
|=> true
|>> x
|=> true
|
|(this is what I expect, true and true = true)
|
|>> x = true and false
|=> false
|>> x
|=> true
|
|But what I’ve got here is “true and false” == false, but it assigns
|true to x. So true and false == false, but really == true… Have I
|lost my mind, should it do this? Does it do it for anyone else? It
|seems weird to me since the first example does what I expect, but the
|second doesn’t…

Precedence.

x = true and false

is parsed as

(x = true) and false

not

x = (true and false)

          matz.
3

It should work if you use && instead of and. Not sure why that is, but
I’m experencing the same thing as you when doing x = true and false,
but it works as expected when using x = true && false.

On 11/28/07, Malcolm L. [email protected] wrote:

=> true
But what I’ve got here is “true and false” == false, but it assigns

–

“Every child has many wishes. Some include a wallet, two chicks and a
cigar, but that’s another story.”

4

On Nov 28, 2007 5:37 PM, Yukihiro M. [email protected] wrote:

x = (true and false)

                                                    matz.

Of course, that makes perfect sense - I guess I am still getting used to
Ruby’s awesome level of flexibility!

Thanks a lot for the quick reply matz, btw - big fan of your work :).

Also, thanks Christian - I will make use of the && in the future!

Thanks,
Malcolm.

5

On Nov 27, 10:43 pm, Christian [email protected] wrote:

It should work if you use && instead of and. Not sure why that is, but
I’m experencing the same thing as you when doing x = true and false,
but it works as expected when using x = true && false.

This also happens in Perl and maybe other similar languages. The
English versions of the logical operators (and, or, not) have lower
precedence than the symbolic versions (&&, ||, !). Why? I don’t know -
the languages were just designed that way.

Jeremy