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### Re^11: Getting for() to accept a tied array in one statement [TANGENT: untie attempted while # references still exist]

by pryrt (Abbot)
 on Apr 18, 2019 at 17:09 UTC Need Help??

I'm not good with tie, but thought I'd take this as a learning exercise. I was surprised by using our @data instead of a fresh anonymous aref for each instance, so I tied @y to the same class to confirm it (confirmed). I wanted to untie those variables and re-use them to tie to a second class that used separate data structures in TIEARRAY (in spoiler; the mods worked as I expected, with separate data structures for @x and @y)... but was surprised at the "untie attempted while 2 inner references still exist" warning when I did the untie. I thought the \$x reference was probably the culprit, so undefined that.... but there was still one remaining inner reference. What is the second inner reference, and where did it come from?

```use strict;
use warnings;
package MyClass; {
use Tie::Array;
our @ISA = ('Tie::Array');
our @data;

#mandatory methods
sub TIEARRAY { my \$class = shift; bless \@data, \$class; @data = @_
+; return \@data }
sub FETCH { my (\$self, \$index ) = @_; print "FETCH(\$index)\n"; ret
+urn \$data[\$index] }
sub STORE { my (\$self, \$index, \$value) = @_; print "STORE(\$index)\
+n"; \$data[\$index] = \$value }
sub FETCHSIZE { print "<FETCHSIZE> "; return scalar @data }
};
package main;

\$|++;
local \$" = ", ";

my @x;

tie @x, "MyClass", 0, 0, 0;
my \$x = \\$x[2];

\$\$x++;
print "x = (@x)\n";

=begin comment

When I first saw the above, it looked like no matter how many items we
+re tied, they would all refer to the same @MyClass::data internal arr
+ay.

The next few lines showed that's true: when I tied @y to the same clas
+s, @x lost its data; and when an element of @y was changed, the same
+happened to @x.

=cut

my @y;
tie @y, "MyClass", 0, 0, 0;
print "y = (@y)\n";
print "x = (@x)\n";

\$y[1] = 3.14;
print "y = (@y)\n";
print "x = (@x)\n";

untie @y;       # gives a warning: untie attempted while 2 inner refer
+ences still exist
undef \$x;       # uncomment to reduce next warning to 1 instead of 2;
+comment to keep next warning at 2
untie @x;       # warning, but with only 1 warning if previous line un
+commented
print "y = (@y)\n";
print "x = (@x)\n";
# so what's the  second inner reference?
• Comment on Re^11: Getting for() to accept a tied array in one statement [TANGENT: untie attempted while # references still exist]

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Re^12: Getting for() to accept a tied array in one statement [TANGENT: untie attempted while # references still exist]
by hdb (Monsignor) on Apr 18, 2019 at 18:03 UTC

Thanks for pointing to this! So it turns out that I am not an expert on classes either...

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