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Postings from May 2003
On Fri, May 23, 2003 at 04:36:47AM -0000, David Muir Sharnoff wrote:
> ---------- begin program ----------
> #!/usr/bin/perl -I.
>
> my $x = 7;
> tie $x, 'Overlay', 8;
> print "tied x = $x.\n";
> untie $x;
> print "untied x = $x.\n";
>
> package Overlay;
>
> sub TIESCALAR
> {
> my $pkg = shift;
> my $y = shift;
> return bless \$y, $pkg;
> }
>
> sub FETCH
> {
> my $self = shift;
> return "<$$self>";
> }
>
> sub STORE { }
> ---------- end program ----------
>
> In the above program, the untie only partially works. After
> the untie, tied($x) no longer returns anything however, if I
> access $x, the value I get is "<8>" instead of the "7" it should
> have reverted to.
There is nothing in the documentation to say that it should
be reverted to its old value.
> If I add UNTIE or DESTROY methods to Overlay, they are called.
>
> If I drop the 'print "tied x = $x.\n";' line then $x remains at "7".
Thats because when FETCH is called perl needs somewhere to place the
result before actually using it. In the case of a tied SCALAR it uses the
scalar that is tied. So there is now way that the old value can be
reverted to. After untie, a scalar will always hold the last value
that was fetched or set.
Graham.
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