Re: set -A

["Bart Schaefer" <schaefer@brasslantern.com>]

On Feb 7, 10:48am, Peter Stephenson wrote:
}
} "Bart Schaefer" wrote:
} > If you've unset arr, then arr is not an array, and hence ${arr[@]} is
} > not an array either, and therefore "${arr[@]}" does not behave like
} > an array; rather, it behaves like a string, so putting it in double
} > quotes yields the empty string.
} 
} But the `@' subscript is not documented to do anything useful for
} strings

That's not strictly true.  The docs say, in consecutive paragraphs:

----------
A subscript of the form `[*]' or `[@]' evaluates to all elements of an
array; there is no difference between the two except when they appear
within double quotes. [...]

Subscripting may also be performed on non-array values, in which case
the subscripts specify a substring to be extracted.
----------

} nor can I see why anyone would assume it was useful in that case

It does NOT say that subscripting non-array values is limited to using
integer ranges; it just says "subscripting may also be performed."

} nor, if they *did* think, that why they would assume that it
} produced a null string instead of the usual elision of the argument.
} (I haven't put that very well.)

You put it well enough, and that last is a valid point.  Since for
foo=(x y z) we have "$foo[@]" equivalent to "x" "y" "z", then given
foo=xyz, should the expectation be that "$foo[@]" is "x""y""z" ?
(Note no word breaks between the quoted substrings.)  That might have
some pretty bizarre side-effects for nested expansions.

} I think we could safely and consistently have a non-existent parameter
} treated as an array in this special case without any negative impact.

It's actually worse than that, though, because ksh treats ALL parameters
as arrays -- in ksh, foo=xyz is the same as foo=(xyz) in zsh, and the
fiction of string variables is maintained by making $foo a reference to
${foo[0]}.  So when KSH_ARRAYS is set, ${foo[1]} (or any number greater
than zero) ought to produce an empty result when used on a scalar.