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Subject: Re: fast subshell
To: zsh-users@zsh.org
References: <df6bc2d6-48ad-d491-355b-0228a4c6e503@eastlink.ca>
 <CAH+w=7Z=9t0hK2CGibSNfN=WWhZzNLq9MHP_N-+s05DgGhq5vQ@mail.gmail.com>
From: Ray Andrews <rayandrews@eastlink.ca>
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Date: Sun, 1 Apr 2018 13:45:46 -0700
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On 01/04/18 11:39 AM, Bart Schaefer wrote:
>
> It's quite possible that doing the memory management for the
> assignment to all_matches in a newly forked process is faster than in
> the original shell (perhaps because the subshell never needs to free
> it again?).  There is also some overhead involved in saving/restoring
> IFS with "local" which you are avoiding.
It's rather interesting.  I suppose the deepest gurus could actually 
discuss the nuts and bolts in detail.  Meanwhile my fears of some 
dreadful overhead are dead.
>
> Also there's really no reason to do both "local IFS=..." and
> "IFS=$OLD_IFS"
I need the thing restored for use latter in the same function. I've 
since seen that:

(
IFS=...
...
)

Somehow screws up, I'm not sure why but it has effects outside the 
parenthesis.  Issues with a subshell within a subshell?  Don't seem right.
>    (){ local IFS=$'\n'; all_matches=( $( whence -mavS $@ ) ) }
I'll try that.
> Or you can do it without changing IFS at all, like this:
>
>    all_matches=( ${(f)"$( whence -mavS $@ )"} )
>
Now that's the 'real' answer.  Direct control within the statement 
itself.   Gotta get used to these nested parameters, it's not really 
that scary.