On Fri, Apr 22, 2011 at 1:15 PM, Kendall Gifford <[email protected]>wrote:
> On Friday, April 22, 2011 10:32:35 AM UTC-6, DK wrote:
>>
>> Just curious if there is a more elegant way to set a variable if it
>> happens to not exist yet. I often find I am doing somthing like the
>> following:
>>
>> regex = ''
>> 10.times { regex += '.*,.*,.*,.*,.*,.*,.*,.*,.*,.*,.*,.*,.*,.*\n' }
>>
>> Is there some prettier way to within the second line create the variable
>> if it does not exist yet? The above just looks ugly. I know I could use a
>> class variable but that also does not seem right as I do not need it to be a
>> class variable:
>>
>> 10.times { @regex += '.*,.*,.*,.*,.*,.*,.*,.*,.*,.*,.*,.*,.*,.*\n' }
>>
>>
> Having no idea what the context is I'll try to answer:
>
> Since the code where you're modifying your variable is w/in a block, any
> variables referenced therein that don't already exist (outside the block)
> won't exist outside the block once after it has run:
>
> > $ cat test.rb
> > 1.times { hi = "hello" }
> > defined?(hi) ? hi += " bye" : hi = "NOT DEFINED"
> > puts hi
> > $ ruby test.rb
> > NOT DEFINED
>
> Thus, for your block to have any effect on local variables that exist in
> the enclosing scope these variables must already "exist" before the block.
> This means the parser must see the local variable (in some context where it
> is clear it is a local variable and not a method call, such as in an
> assignment statement) before the block definition in the enclosing scope.
>
> So, assuming I understand your intent, the answer is no. The local must
> already be defined (whether initialized with an actual value is another
> matter (*see example below)) or you should use an instance, class, or
> global.
>
> * (
> > $ cat test.rb
> > hi = nil if false # defines hi even though assignment never executed
> > 1.times { hi = "hello" }
> > defined?(hi) ? hi += " bye" : hi = "NOT DEFINED"
> > puts hi
> > $ ruby test.rb
> > hello bye
>
> I don't know if this helps any or not...
>
Thanks Kendall... actually I think I confused things by putting the block
but I think the answer is still pretty much the same for a case such as the
following, that if I did not want to first create the variable by
assignment, that I should use an instance, class or global as you say.
regex = ''
regex += 'something'
...
regex += 'something else'
...
regex += 'and another something'
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