From: Josh Cheek <josh.cheek@...>
Date: 2011-04-05T12:30:47+09:00
Subject: Re: pipe question

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On Mon, Apr 4, 2011 at 7:12 PM, 7stud -- <bbxx789_05ss@yahoo.com> wrote:

> Josh Cheek wrote in post #990762:
> >
> > 3) For some reason that I don't know (probably interpreter magic) an
> > uninitialized variable can be referenced in a boolean equation and it
> > will
> > evaluate to nil.
> >
> > first_name = first_name || "" # => ""
> > first_name = "josh"
> > first_name = first_name || "" # => "josh"
> >
> >
> > So, it will set the variable to the empty string, if the variable is
> > undeclared, or false , or nil.
>
> I think the story goes something like this:  when the parser sees any
> 'name =' expression, name gets entered into the symbol table.
> Thereafter, you will no longer get an exception when referencing the
> variable.  In your code, the parser sees 'first_name =', so first_name
> is entered into the symbol table, and then when ruby executes your code,
> the expression on the right hand side of the equals sign is executed.
>
>
Makes sense, and passed the test I constructed to invalidate it:
lhs = rhs || "pass"
lhs # =>
# ~> -:1:in `<main>': undefined local variable or method `rhs' for
main:Object (NameError)


I probably never figured that out because it depends on the variable type,
for example:
lhs = @rhs || "pass" # => "pass"
and
lhs = $rhs || "pass" # => "pass"



> Here is an example that might prove illustrative:
>
> if 1 > 10
>  x = 'hello'  #never executes
> end
>
> puts x  #=> nil
> puts y  #=> undefined local variable or method `y'
>        #for main:Object (NameError)
>
>
Good thought. I'm honestly surprised that works! I guess it must add x to
the symbol table at parse time.

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