Array values and parameter expansion specs

["Bart Schaefer" <schaefer@xxxxxxxxxxxxxxxxxxxxxxx>]

There isn't much documentation in zshexpn.man concerning which of the SPEC
forms can be used with array expressions.  For example, ${#NAME} describes
what happens if NAME is an array, and there are a few mentions of NAME[@],
but otherwise there's silence.  The stuff in zshparam.man (and the "Array
parameters" section of zsh.info) is no more helpful.

Consider:

zsh% foo=(1 2 3)
zsh% echo ${foo[2]:+whee}
whee
zsh% echo ${foo[2]:-whee}
2
zsh% echo ${foo[2]:=whee}
zsh: closing brace expected
zsh%

What's the distinction?

-- 
Bart Schaefer                             Brass Lantern Enterprises
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