Dear Monks,

I have just encountered the following strangeness:
A subroutine appears to 'remember' a my variable from it's previous invocation:

The variable here is a code ref: 
# A 'wannabe' foreach, which:
#   - takes a CODE ref as an optional first argument
#   - applies it to the rest of the args
#   - If no CODE ref was passed, then it uses a closure of its 
#     own that simply shoves all the args into an accumulator list
#     which it just dumps to STDERR
sub wannabe_foreach {
    my $func = shift if ref $_[0] eq 'CODE'; # optional code-ref
    # Funkiness:  $func has a value if:
    #                 (a) the user gave it one; 
    #                     (User thinks closures are funky)
    #                 (b) it mysteriously has a value.
    #                     (many people would call that 'funky')
    warn "my func is funky!\n" if $func;
    my @list = @_;

    my @accumulator = ();
    $func = sub { push @accumulator, shift } unless $func;

    $func->($_) for @list;

    warn join ",", @accumulator if @accumulator;

}

wannabe_foreach(1..3); # Works. Warns: '1,2,3 at foo.pl line ...'
wannabe_foreach(1..4); # Gets funky.

# Still funky, but at least the passed code ref is invoked.
# wannabe_foreach(sub { print shift }, 1..7); print "\n";
# Plain funky again. 
# wannabe_foreach(1..7);

[download]

A cursory debugging shows that the line 

my $func = shift if ref $_[0] eq 'CODE'; # optional code-ref

[download]
Gets funny - $func retains a reference to the closure created in the previous invocation. Looks like the compiler is too eager to optimize the closure instances?

Well whatever the reason is, the fix was simply: 

#my $func = shift if ref $_[0] eq 'CODE';
my $func  = ref $_[0] eq 'CODE' ? shift() : undef;

[download]

Strange. I mean, one would expect that $func end up as 'undef' in any case right? And even then, why does it end up as a reference to the old $func?

So - I suspect some glaring 'overlooking the obvious' mistake on my part, but not having found a reason that I understand yet, I thought I'd ask you all.

In reply to Unforgettable Closures? by faiz

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