Hello Laurent_R,

You understood me correctly, and it appears I was wrong: you have shown that it is possible to build a closure using function templates. But I note that, to get the syntax to work, you had to remove the local from the definition of *inner within sub make_adder, and that makes *inner a package global sub. In fact, what sub make_adder returns is simply the string *main::inner. So we can dispense with make_adder’s return value and the assignments to *f1 and *f2 altogether:

#! perl
use strict;
use warnings;
use v5.14;

make_adder(20);
say  inner(10);
make_adder(25);
say  inner(10);

sub make_adder
{
    my      $addpiece = shift;
    print "\$addpiece = $addpiece\n";
    *inner = sub { return shift() + $addpiece; };
}

[download]

Output:

13:02 >perl 1102_SoPW.pl
$addpiece = 20
30
$addpiece = 25
Subroutine main::inner redefined at 1102_SoPW.pl line 15.
35

13:02 >

[download]

This approach is inferior to the standard technique (references to anonymous subroutines) in at least two ways:

  1. Each call to make_adder creates a new closure, and the previous closure is no longer available (hence the warning message).
  2. The memory allocated to $addpiece will never be garbage collected as long as the script is running.

Hope that helps,

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

In reply to Re^3: closures: anonymous subs vs function templates? by Athanasius
in thread closures: anonymous subs vs function templates? by 5haun

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