Re: Should [[ -v 1 ]] be supported?

[Martijn Dekker]

Op 27-12-18 om 19:22 schreef Chet Ramey:
> On 12/26/18 10:49 PM, Peng Yu wrote:
>
> > Although [[ -z ${1+s} ]]  and (($#)) works for testing if $1 is set,
> > neither of them are uniformly better performance wise. In this case,
> > should [[ -v 1 ]] be supported?
>
> So you're saying that neither of the existing options performs better
> than the other, though they both perform well, so we should add some
> new capability just because? That's a particularly poor argument.

Consistency might be a better argument. If [[ -v foo ]] is equivalent to 
[[ -n ${foo+s} ]] for variables (with the advantage that you don't need 
'eval' to handle arbitrary values of 'foo'), then perhaps it's not 
unreasonable to expect [[ -v 1 ]] to be equivalent to [[ -n ${1+s} ]].

FWIW, zsh and mksh do support this; ksh93 doesn't.

- M.