[MacRuby-devel] Weird behaviour for a weird line of code

[Mark Rada]

On 2010-11-15, at 4:50 PM, Ryan Davis wrote:

> 
> On Nov 14, 2010, at 18:37 , Mark Rada wrote:
> 
>> Now, when I try this out in macirb: (Case #3)
>> 
>>  require 'uri'
>>  test = URI.parse url unless (url = 'http://macruby.org/').nil?  # error
>>  test = URI.parse url unless (url = 'http://wikipedia.org/').nil? # works
>> 
>> If it doesn't work in the second case, why does it start working in the third case?
> 
> First off, I hate this style of coding. If you didn't assign in a conditional you'd avoid all of this crap to begin with. Assigning in conditionals is just a sloppy and error prone way of coding and you should avoid it. This has been a known anti-pattern in any algol-esque language since at least the 80s.
> 
> That said... This actually has nothing to do with macruby and is an effect of the ruby parser. It is about variable visibility.

Ah, that is what I was not understanding. Thanks for explaining.

> 
> In case 3:
> 
> + The first line has "URI.parse url" followed by "unless (url = ...).nil?"
>  + The first 'url' is actually parsed as a method call because the word has never been seen before and wasn't added to the variable table. The second url DOES add url to the variable table.
> + The second line has the same thing, but by now, "url" has been added to the variable table. This lets everything be parsed as a variable at parse time.