Michael Hollins
8/6/2007 11:38:00 PM
Tom Werner wrote:
> Nicolas Lehuen wrote:
>> Hi,
>>
>> I've just lost a few hours on this strange behaviour (bug ?).
>> Apparently it is caused by some kind of operator precedence
>> thingamagic. My original code was of course much more complicated, so
>> finding the problem wasn't easy (I first thought my code was
>> buggy...). Here is a piece of minimal code that reproduces the
>> problem :
>>
>> 8<-------------8<-------------8<-------------8<-------------
>>
>> C:\temp>ver
>>
>> Microsoft Windows [version 6.0.6000]
>>
>> C:\temp>ruby -v
>> ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-mswin32]
>>
>> C:\temp>type bug.rb
>> sum1 = 1 + 1 + 1
>>
>> puts sum1
>>
>> sum2 = (
>> 1
>> + 1
>> + 1
>> )
>>
>> puts sum2
>>
>> C:\temp>ruby bug.rb
>> 3
>> 1
>>
>> 8<-------------8<-------------8<-------------8<-------------
>>
>> >From now on I promise I'll remember that you cannot safely use multi-
>> line parenthesis expressions in Ruby ; I just would like to understand
>> what this code means to Ruby, if it's not "give me the result of 1 + 1
>> + 1".
>>
>> The same takes place in irb :
>>
>> C:\temp>irb
>> irb(main):001:0> sum1 = 1 + 1 + 1
>> => 3
>> irb(main):002:0> sum2 = (
>> irb(main):003:1* 1
>> irb(main):004:1> + 1
>> irb(main):005:1> + 1
>> irb(main):006:1> )
>> => 1
>> irb(main):007:0> op3 = (
>> irb(main):008:1* 1
>> irb(main):009:1> * 3
>> irb(main):010:1> * 9
>> irb(main):011:1> )
>> SyntaxError: compile error
>> (irb):9: syntax error, unexpected '\n', expecting tCOLON2 or '[' or
>> '.'
>> from (irb):11
>> from :0
>>
>> Duh ! This must mean something, but what ?
>>
>> Regards,
>>
>> Nicolas Lehuen
>>
>>
>>
>>
> +1 is a valid ruby statement by itself. In order for the interpreter to
> realize that your statement continues onto another line, you must end
> the line with an operator that begs for more. In your case, moving the
> pluses up to the previous lines will work:
>
> irb(main):003:0> (1 +
> irb(main):004:1* 1 +
> irb(main):005:1* 1)
> => 3
>
> You get that error in irb with multiplication because * 3 is not a valid
> ruby statement by itself (remember that + 1 is valid, meaning simply, 1).
>
Are there any interesting uses of
+ x
as a statement on its own, or is it likely that
it's a programmer error 99 times out 100? If the latter, perhaps it's worth
the ruby interpreter emitting a warning when it sees such constructs, much
like the warning you get when you don't use parantheses around argument lists
in certain situations.
I'm happy to be told that there are valid uses of "+ x". I'm still learning something
new about ruby every day.
cheers,
mick