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Re: subroutine refs

by broquaint (Abbot)
on Nov 30, 2007 at 18:19 UTC ( #654158=note: print w/replies, xml ) Need Help??

in reply to subroutine refs

You can safely create a reference to a subroutine by name and the execute that e.g
use strict; sub dynamic { print "Mmm, dynamic.\n"; } my $name = 'dynamic'; my $subref = \&$name; &$subref();


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Re^2: subroutine refs
by blokhead (Monsignor) on Nov 30, 2007 at 18:50 UTC
    I find this very surprising. But I checked it and it apparently works.

    Why does this give an error:

    use strict; sub dynamic { print "hello\n"; } my $name = "dynamic"; &$name();
    .. and yet this is ok? (they differ only in the last line)
    use strict; sub dynamic { print "hello\n"; } my $name = "dynamic"; &{ \&$name }();
    Before seeing this, I would have bet anything that the &{\&{ ... }} operation was absolutely the same as &{...} (barring weird action-at-a-distance caused by tying, overloading, etc). In fact, I'm not sure whether to consider this a bug or not. Indeed, what is \&$name doing other than "using string as a subroutine ref", which is outlawed under strict refs?

    Yet a similar idea with other kinds of refs doesn't do this. Both of these examples fail under strict refs (in my mind because @{\@{...}} is unconditionally the same thing as @{...} ):

    use strict; our @dynamic = ("hello\n"); my $name = "dynamic"; print @$name;
    use strict; our @dynamic = ("hello\n"); my $name = "dynamic"; print @{ \@$name };
    My conclusion is that there is an important distinction between naming a subroutine and invoking it, which is manifested bizarrely by different behaviors in the \&{blah} and &{blah} mechanisms.


Re^2: subroutine refs
by HelenCr (Monk) on Sep 14, 2013 at 11:44 UTC
    broquaint: This is amazing. I was looking for such a solution for a while.

    Thinking about it, is this canonical? (namely, documented)? or is it a quirk (an oversight in the Perl language design?)

      Removing the intermediate assignment to $name, broquaint’s code simplifies to:

      use strict; my $subref = \&{'dynamic'}; &$subref(); sub dynamic { print "Mmm, dynamic.\n"; }

      which is explicitly documented as an exception to the normal behaviour of strict 'refs' (see strict):

      There is one exception to this rule:

      $bar = \&{'foo'}; &$bar;

      is allowed so that goto &$AUTOLOAD would not break under stricture.

      So, yes, this is canonical.

      Hope that helps,

      Athanasius <°(((><contra mundum Iustus alius egestas vitae, eros Piratica,

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