# Unlogical?

**URL:** <https://www.ruby-forum.com/t/unlogical/96934>\
**Category:** Ruby\
**Created:** [December 9, 2005, 8:40am UTC](https://www.ruby-forum.com/t/unlogical/96934 "2005-12-09T08:40:27Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![christer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a5b964/32.png) [@christer](https://www.ruby-forum.com/u/christer)\
**Post date:** [December 9, 2005, 8:40am UTC](https://www.ruby-forum.com/t/unlogical/96934/1 "2005-12-09T08:40:27Z")

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Hmm, why are these two assertions breaking?

def test\_strange  
assert\_equal true, true && true  
assert\_equal false, true && false  
assert\_equal false, false && true  
assert\_equal false, false && false

```
assert_equal true, true and true
assert_equal false, false and true
assert_equal false, false and false
assert_equal false, true and false # breaks

assert_equal true, true || true
assert_equal true, true || false
assert_equal true, false || true
assert_equal false, false || false

assert_equal true, true or true
assert_equal true, true or false
assert_equal false, false or false
assert_equal true, false or true # breaks

```

end

Christer

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**Author:** ![christer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a5b964/32.png) [@christer](https://www.ruby-forum.com/u/christer)\
**Post date:** [December 9, 2005, 8:54am UTC](https://www.ruby-forum.com/t/unlogical/96934/2 "2005-12-09T08:54:27Z")

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On Dec 8, 2005, at 11:40 PM, Christer N. wrote:

> Hmm, why are these two assertions breaking?

assert\_equal false, true or false  
assert\_equal(false, true) or false  
assert\_equal(false, (true or false))

jeremy  
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<div class="post-metadata">

**Author:** ![christer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a5b964/32.png) [@christer](https://www.ruby-forum.com/u/christer)\
**Post date:** [December 9, 2005, 8:54am UTC](https://www.ruby-forum.com/t/unlogical/96934/3 "2005-12-09T08:54:28Z")

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On Dec 9, 2005, at 2:40 AM, Christer N. wrote:

> ```
> assert_equal true, false or true # breaks
> 
> ```

or has relatively low precedence. I imagine ruby sees assert\_equal  
(true, false) or true.  
Try throwing in some parens eg. assert\_equal(true, false or true)

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**Author:** ![christer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a5b964/32.png) [@christer](https://www.ruby-forum.com/u/christer)\
**Post date:** [December 9, 2005, 8:58am UTC](https://www.ruby-forum.com/t/unlogical/96934/4 "2005-12-09T08:58:32Z")

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On Fri, 9 Dec 2005, Christer N. wrote:

> Hmm, why are these two assertions breaking?

> assert\_equal false, true && false  
> assert\_equal false, true and false # breaks

‘&&’ and ‘and’ have a different level of precedence, as such, the two  
statements are read as:

```
  assert_equal (false, true && false)
  assert_equal (false, true) and false

```

Similar for the ‘or’. In the case of the or, you could even observe this  
in irb:

```
irb(main):004:0> puts false || true
true
=> nil
irb(main):005:0> puts false or true
false
=> true

```

Since the ‘or’ has a lower precedence than the ‘||’, the ‘or’ is applied  
to the result of puts, not to the parameter ‘false’.

Benedikt

ALLIANCE, n. In international politics, the union of two thieves who  
have their hands so deeply inserted in each other’s pockets that  
they cannot separately plunder a third.  
(Ambrose Bierce, The Devil’s Dictionary)

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<div class="post-metadata">

**Author:** ![christer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a5b964/32.png) [@christer](https://www.ruby-forum.com/u/christer)\
**Post date:** [December 9, 2005, 10:03am UTC](https://www.ruby-forum.com/t/unlogical/96934/5 "2005-12-09T10:03:50Z")

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Christer N. wrote:

> Maybe it has to do with parallell assignment, as the comma is used  
> there.

I don’t think it’s that.

> My workaround will be to use “&&”

Parens will work around either.

&&, || “give” you parenthesised left and right terms -  
and, or don’t.

```
 a && b equates with: (a and b)

     r = true and false

```

equates with:  
((r = true) and false)

Test:  
r2 = ((r = true) and false)

p [r, r2] #=\> [true, false]

The following won’t make anything clearer but it  
may help you to understand why it’s not clear 😉

r = true and false ; p r #=\> true  
r = true and (false) ; p r #=\> true  
r = (true ) and false ; p r #=\> true  
r = true && false ; p r #=\> false  
r = ( true and false ) ; p r #=\> false  
r = ( true and (false)) ; p r #=\> false  
r = ((true ) and false ) ; p r #=\> false  
puts  
r = false or true ; p r #=\> false  
r = false or (true ) ; p r #=\> false  
r = (false) or true ; p r #=\> false  
r = false || true ; p r #=\> true  
r = ( false or true ) ; p r #=\> true  
r = ( false or (true )) ; p r #=\> true  
r = ((false) or true ) ; p r #=\> true

daz

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<div class="post-metadata">

**Author:** ![christer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a5b964/32.png) [@christer](https://www.ruby-forum.com/u/christer)\
**Post date:** [December 10, 2005, 4:49am UTC](https://www.ruby-forum.com/t/unlogical/96934/6 "2005-12-10T04:49:54Z")

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On Dec 9, 2005, at 3:51 AM, Christer N. wrote:

> ruby wrote:
> 
> > ```
> > assert_equal (false, true && false)
> > assert_equal (false, true) and false
> > 
> > ```
> 
> Pickaxe does not list “,” in the operator precedence table.

Because ‘,’ is not an operator. It is an argument separator.

> > assert\_equal (false, true) and false

is the same as:

```
assert_equal(false,true) and false

```

I think the space between the method name and the opening  
paren of the argument list is confusing you.

Gary W.

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<div class="post-metadata">

**Author:** ![christer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a5b964/32.png) [@christer](https://www.ruby-forum.com/u/christer)\
**Post date:** [December 9, 2005, 9:50am UTC](https://www.ruby-forum.com/t/unlogical/96934/7 "2005-12-09T09:50:56Z")

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ruby wrote:

> ```
> assert_equal (false, true && false)
> assert_equal (false, true) and false
> 
> ```

Pickaxe does not list “,” in the operator precedence table.

&& || .. ... ? : = etc \<\<= etc defined? not or and

The only operator relating to “,” here is “=”.  
Maybe it has to do with parallell assignment, as the comma is used  
there.

a, b = false, true

My workaround will be to use “&&”

Christer