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

I was just playing around with Memoize::Expire and did a one line test. It worked as expected when I use "print f().$/" but does not expire the memoized function f() when I use "say f();" 

perl -MMemoize -MMemoize::Expire -E 
  "sub f {int rand 100};
   tie my %cache => 'Memoize::Expire',LIFETIME=>2; 
   memoize 'f',SCALAR_CACHE => [HASH => \%cache ];
   for (1..10) {print f().$/; sleep 1}"
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perl -MMemoize -MMemoize::Expire -E 
  "sub f {int rand 100};
   tie my %cache => 'Memoize::Expire',LIFETIME=>2; 
   memoize 'f',SCALAR_CACHE => [HASH => \%cache ];
   for (1..10) {say f(); sleep 1}"
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After a bit of tracking down I found it only works when the function is called in scalar context. For instance say f()+0; works fine.

I tried altering my invocation of memoize to use LIST_CACHE rather than SCALAR_CACHE but then it crashes

Can't use string ("ARRAY(0x9c7494)") as an ARRAY ref while "strict refs" in use at C:/Perl516/lib/Memoize.pm line 258.

Does anyone know if Memoize::Expire can be got to work in list context? Or do I have to roll my own if I need that

Cheers,
R.

Pereant, qui ante nos nostra dixerunt!

Replies are listed 'Best First'.
Re: Memoize::Expire oddity
by McA (Priest) on Aug 14, 2013 at 15:47 UTC

    Hi,

    looking at the code of Memoize::Expire on line 56 of the current version 

    $self->{C}{$key} = $header . $value;

    [download]
    let me assume that there is a bug or it was never intended to use this module in list context. In your case $value is an array ref, which gets stringified by this operation. When fetching this value you get the error you presented.

    I'm sorry, but in this case I can only cite the man page to this module

    This module is experimental, and may contain bugs. Please report bugs to the address below.

    Best regards
    McA

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Re: Memoize::Expire oddity
by ryanc (Monk) on Aug 15, 2013 at 17:51 UTC
    My first guess was to add LIST_CACHE => 'MERGE' to your memoize options. I tested it this way and your second example seems to work now. I didn't make any other changes.

    I'm running Perl 5.14.2.
[reply]
[d/l]

      I tried MERGE too and got the same error. I was using 5.16.2 on Windows. That's my work box. I'm home now on Linux, MERGE is also not helping me. am I using the option wrongly? 

      r@Che ~ $ perl -MMemoize -MMemoize::Expire -E "sub f {int rand 100}; \
          tie my %cache => 'Memoize::Expire',LIFETIME=>2,LIST_CACHE=>'
+MERGE';\
          memoize 'f',SCALAR_CACHE => [HASH => \%cache ];\
          for (1..10) {say f(); sleep 1}"
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r@Che ~ $ perl -v

This is perl 5, version 14, subversion 2 (v5.14.2) built for x86_64-li
+nux-gnu-thread-multi
(with 65 registered patches, see perl -V for more detail)

Copyright 1987-2011, Larry Wall

Perl may be copied only under the terms of either the Artistic License
+ or the
GNU General Public License, which may be found in the Perl 5 source ki
+t.

Complete documentation for Perl, including FAQ lists, should be found 
+on
this system using "man perl" or "perldoc perl".  If you have access to
+ the
Internet, point your browser at http://www.perl.org/, the Perl Home Pa
+ge.

      [download]

      Cheers,
      R.

      Pereant, qui ante nos nostra dixerunt!
[reply]
[d/l]
        $ perl -MMemoize -MMemoize::Expire -E " \
    sub f { int rand 100 }; \ 
    tie my %cache => 'Memoize::Expire', LIFETIME => 2; \
    memoize 'f', LIST_CACHE => 'MERGE', \
                 SCALAR_CACHE => [ HASH => \%cache ]; \
    for (1..10) { say f(); sleep 1 }"
62
62
56
56
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85
85
42

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