Memoize::Expire oddity

[Random_Walk]

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}"
16
16
95
95
61
61
62
62
93
93

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}"
89
89
89
89
89
89
89
89
89
89

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.

[McA]

Hi,

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

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

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

[ryanc]

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.

[Random_Walk]

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}"
45
45
45
45
45
45
45
45
45
45
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.

Cheers,
R.

[ryanc]

$ 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
39
39
85
85
42