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From: Bart Schaefer <schaefer@brasslantern.com>
Message-Id: <160205091543.ZM29723@torch.brasslantern.com>
Date: Fri, 5 Feb 2016 09:15:43 -0800
In-Reply-To: <CAKc7PVCDHQDc=sby5wGNEtWCA6omFhmP8uPWbsPXwTQv9tDqFw@mail.gmail.com>
Comments: In reply to Sebastian Gniazdowski <sgniazdowski@gmail.com>
        "Should (t)path = array-unique-special work this way" (Feb  5,  2:45pm)
References: <CAKc7PVCDHQDc=sby5wGNEtWCA6omFhmP8uPWbsPXwTQv9tDqFw@mail.gmail.com>
To: Zsh hackers list <zsh-workers@zsh.org>
Subject: Re: Should (t)path = array-unique-special work this way
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On Feb 5,  2:45pm, Sebastian Gniazdowski wrote:
}
} typeset -U path
} PATH="$PATH:/component/nr1"
} path+="/component/nr2"
} PATH="/component/nr2:$PATH"
} print "${(t)path}"
} declare -p path

I'm not really sure what question(s) you're asking.

Aside:
 Although it works to append to an array with path+="/component/nr2",
 it's really not good form.  Get used to path+=("/component/nr2") and
 you'll have much less trouble later.

Back to main topic:

} Outputs:
} array-unique-special

So far so good.

} typeset -a path
} path=( /component/nr2 /usr/local/bin /usr/bin /bin /usr/games /component/nr1 /component/nr2 )

For 5.3, this will change to

typeset -a path=( /component/nr2 /usr/local/bin /usr/bin /bin /usr/games /component/nr1 /component/nr2 )

Other things you might be asking about:

Q: Why is nr2 repeated when path is declared -U ?
A: Because it's repeated in $PATH.  Array uniqueness of tied arrays is
   only applied when assigning to the array; when assigning to the tied
   scalar, the array faithfully copies the value of the scalar.  If this
   were not the case, you could end up with a feedback loop (scalar is
   changed -> array uniquifies -> scalar changes again -> etc.).  This
   in turn is because scalars don't have a "uniqueness" property, so if
   the user is explicitly assigning to the scalar then we presume it is
   expected to reflect the value so assigned.

Q: Why doesn't -U appear in the "declare -p" output?
A: Good question.  It doesn't appear for non-special arrays either.  It
   may be intentional because -U isn't a POSIX-supported option, but I
   suspect it's just an accidental omission.