From: Dave Aronson <rubytalk2dave@...>
Date: 2013-01-21T05:21:43+09:00
Subject: Re: question about string concatenation

On Sun, Jan 20, 2013 at 3:08 PM, David Richards <lists@ruby-forum.com> wrote:

> I'm puzzled about why the following happens (I'm using v1.9.3):
>
> s = "[" 9.to_s "]"  # error
>
> These other two concatenation constructs appear to work fine:
>
> s = "[" + 9.to_s + "]"
> s = "[" << 9.to_s << "]"
>
> What's the key concept I'm missing here?

Looks like you're trying to "autoconcatenate" three strings.  (If that
wasn't a word before, it is now!)  This works fine IF they're all
literals, like this:

1.9.3p194 :001 > "1" "2" "3"
 => "123"
1.9.3p194 :002 > "1" '2' "3"
 => "123"

But if one of them is not a literal, Ruby won't autoconcatenate it:

1.9.3p194 :003 > "1" 2.to_s "3"
SyntaxError: (irb):3: syntax error, unexpected tINTEGER, expecting $end
"1" 2.to_s "3"
     ^
	from /Users/dave/.rvm/rubies/ruby-1.9.3-p194/bin/irb:16:in `<main>'

My SWAG would be that autoconcatenation takes place at the parser
level, and using anything other than a literal would require actual
evaluation, so it can't be done at that level, only after the thing is
actually evaluated.  At that level, though, it breaks the Ruby syntax
rules, which require that you put some kind of operator between items.
 That's why your other examples *do* work, as you've inserted the + or
<< operators.

-Dave

-- 
Dave Aronson, the T. Rex of Codosaurus LLC,
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