Strange behaviour of Tkx in combination with Storable

JanLaloux has asked for the wisdom of the Perl Monks concerning the following question:

I have a peculiar problem using module Tkx in combination with module Storable. The purpose is to store all parameters entered by a user in a Tk interface in a file so that it can be loaded the next time when the program is started again.

I have simplified the code here, there is only one parameter $Value and a simple Tk screen with only one entry field linked to $Value. I first store and retrieve $Value and this works OK. Then I change the value with the Tk screen and then things go strange:

my $Value = 666;
store( \$Value, 'param.ini' );
# The file viewed in Wordpad shows 'pst0    12345678š  '

my $pRPar = retrieve('param.ini');
$Value = $$pRPar;
print("$Value\n"); # Prints '666'

my $MainWindow = Tkx::widget->new('.');
my $Entry = $MainWindow->new_ttk__entry(-textvariable => \$Value);
$Entry->g_grid(-row => 1, -column => 1);
Tkx::MainLoop(); # Change the value into '111' and close the window
print("$Value\n"); # Prints '111', so this is OK. But...

store( \$Value, 'param.ini' );
# The file viewed in Wordpad shows now 'pst0    12345678Tcl::
+Var   Tcl¾^    ::perl::SCALAR(0x3b54b38)'
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So the first time the value is stored correctly (if you use a string instead of an integer you will see the string value in the file). The second time you see strange things appear such as 'Tcl::Var' and '::perl::SCALAR(0x3b54b38)'.

Any idea what's happening here?

Comment on Strange behaviour of Tkx in combination with Storable Download Code

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Re: Strange behaviour of Tkx in combination with Storable by aitap (Curate) on Jan 03, 2014 at 20:36 UTC
That's probably because your `$Value` becomes an object with overloaded stringification, so it prints 111, but really is a reference to a scalar blessed into Tcl::Var package. Try storing `"$Value"` instead of just `$Value` to force stringification and store only the value you need.	[reply] [d/l] [select]
Re^2: Strange behaviour of Tkx in combination with Storable by JanLaloux (Novice) on Jan 04, 2014 at 10:37 UTC
Thanks aitap. What I forgot to mention explicitely is that Storable crashes when retrieving the references to the Tcl::Var objects. I could avoid this by copying all parameters to new variables first and store those, but this is rather ugly. Do you see another way to make Storable see the correct data structure?	[reply]
Re^3: Strange behaviour of Tkx in combination with Storable by aitap (Curate) on Jan 04, 2014 at 11:51 UTC
You can make a reference to a stringified copy of your variable on the fly: `store \"$Value", $filename`, or, if you are storing a data srtucture, `store { var => 1, anothervar => "$Value", ... }, $filename`. Quotes explicitly transform anything into a string, and no object can survive that.	[reply] [d/l] [select]
Re: Strange behaviour of Tkx in combination with Storable by zentara (Cardinal) on Jan 05, 2014 at 12:07 UTC
You might be interested in looking at ztkdb, where I do essentially the same thing with Tk instead of Tkx. I'm not really a human, but I play one on earth. Old Perl Programmer Haiku ................... flash japh	[reply]