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From: Peter J. Holzer on 21 Apr 2010 18:56
On 2010-04-21 15:42, Ben Morrow <ben(a)morrow.me.uk> wrote:
> File::Copy (at least, v2.14, which comes with 5.10.1) uses
>
> my $fh = \do { local *FH };
>
> which is how you created a scoped filehandle before 5.6. At least in
> modern perls, these handles will also auto-close on scope exit.

Ah, nice trick. Too bad I learn about it only now that I don't need it
any more :-).

hp
From: Uri Guttman on 21 Apr 2010 19:09
>>>>> "PJH" == Peter J Holzer <hjp-usenet2(a)hjp.at> writes:

PJH> On 2010-04-21 15:42, Ben Morrow <ben(a)morrow.me.uk> wrote:
>> File::Copy (at least, v2.14, which comes with 5.10.1) uses
>>
>> my $fh = \do { local *FH };
>>
>> which is how you created a scoped filehandle before 5.6. At least in
>> modern perls, these handles will also auto-close on scope exit.

PJH> Ah, nice trick. Too bad I learn about it only now that I don't need it
PJH> any more :-).

even older or at least the same age is the Symbol module which basically
does the same thing. it first increments a string to create a new
symbol, then allocates that glob and deletes the symbol. you get back
the anon glob which can be used for any handle. the above code does a
similar but shorter trick in temporarily allocating a new glob (the
local) and then getting a reference to it while the local leaves
scope. so no one else has access to the new glob which makes it anon
too.

uri

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From: Ben Morrow on 21 Apr 2010 19:34

Quoth "Peter J. Holzer" <hjp-usenet2(a)hjp.at>:
> On 2010-04-21 15:42, Ben Morrow <ben(a)morrow.me.uk> wrote:
> > File::Copy (at least, v2.14, which comes with 5.10.1) uses
> >
> > my $fh = \do { local *FH };
> >
> > which is how you created a scoped filehandle before 5.6. At least in
> > modern perls, these handles will also auto-close on scope exit.
>
> Ah, nice trick. Too bad I learn about it only now that I don't need it
> any more :-).

It's still occasionally useful, for instance with IPC::Open3 which can't
autoviv handles (because it already had a meaning for undef before 5.6).
As Uri says, you can also use the Symbol module; in principle if you're
creating lots of filehandles you could use Symbol::geniosym or

do { local *FH; *FH{IO} }

to save a bit of memory. (An IO ref ought to work as a filehandle
everywhere a globref does, and you save the GV+GP+SV that you aren't
using.)

Ben

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