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From: Micah Elliott <micah@membean.com>
Date: Fri, 12 Aug 2011 17:24:14 -0700
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Message-ID: <CAELbujo=KyJyzzo1vW+ydLVA=PddguguXkBr7yN3zvmOgmYFpQ@mail.gmail.com>
Subject: Idiom for booleans
To: zsh-users@zsh.org
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Hi! I'm trying to figure out if the $+ expansion, as in ${+param}, is
worth making use of. What idiom do you use for it? I could see it as a
boolean for testing flags. As in:

  % verbosity=3Dhigh myscript.zsh
  ...
  (( $+verbosity )) && print chatty
  chatty

  % unset verbosity  # uh-oh
  % (( $+verbosity )) && print chatty  # should this work?
  ((: command not found

I did see this idiom used in the Zsh Guide
(http://zsh.sourceforge.net/Guide/zshguide03.html as: (( OPTIND > 1 ))
&& shift $(( OPTIND - 1 )) ) -- is that a bug?

I suppose it boils down to understanding (explanation welcome here):

  % (( 0 ))
  ((: command not found
  % (( 1 ))  # ok

Wrapping in "if" makes it work too, but just feels tedious:

  % if (( 0 )); then print i say nothing; fi

----

I could make the boolean work by adding a fall-thru:

  % (( $+verbosity )) && print chatty || :

but that feels rotten. Or I could use:

  % [[ $+verbosity =3D=3D 1 ]] && print chatty

but that doesn't seem any better than the more common and simpler:

  % [[ -n $verbosity ]] && print chatty

So is there some concise idiomatic way of making use of $+ ? Or is
this last line the better way to make such tests?

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