From: Mauricio Fernandez <mfp@...>
Date: 2006-02-02T08:48:17+09:00
Subject: Re: memoize to a file

On Thu, Feb 02, 2006 at 06:49:49AM +0900, Daniel Berger wrote:
> > and it instead of silently failing I now see the error message: "in `load':
> > marshal data too short (ArgumentError)"
> >
> > My questions:
> > 1  What is causing this error? (possibly Windows related?)
> 
> That is odd.  I've run it on Windows with no trouble in the past.  

(FTR: file not opened in binary mode, [177651])
> Is it possible you ran this program using 1.8.2, downloaded 1.8.4, then
> re-ran the same code using the same cache?  It would fail with that
> error if such is the case, since Marshal is not compatible between
> versions of Ruby - not even minor versions.

The Marshal format hasn't changed for a while:

batsman@tux-chan:~/Anime$ ruby182 -v -e 'p [Marshal::MAJOR_VERSION, Marshal::MINOR_VERSION]'
ruby 1.8.2 (2004-12-25) [i686-linux]
[4, 8]
batsman@tux-chan:~/Anime$ ruby -v -e 'p [Marshal::MAJOR_VERSION, Marshal::MINOR_VERSION]'
ruby 1.8.4 (2005-12-24) [i686-linux]
[4, 8]

Also note that ruby can read Marshal data in older formats if the
MAJOR_VERSION hasn't changed (i.e. if only the MINOR_VERSION was increased):


    if (major != MARSHAL_MAJOR || minor > MARSHAL_MINOR) {
	rb_raise(rb_eTypeError, "incompatible marshal file format (can't be read)\n\
\tformat version %d.%d required; %d.%d given",
		 MARSHAL_MAJOR, MARSHAL_MINOR, major, minor);
    }
    if (RTEST(ruby_verbose) && minor != MARSHAL_MINOR) {
	rb_warn("incompatible marshal file format (can be read)\n\
\tformat version %d.%d required; %d.%d given",
		MARSHAL_MAJOR, MARSHAL_MINOR, major, minor);
    }


(after some searching...)

Back in Apr. 2001, matz said that "Marshal should not change too much
(unless in upper compatible way)" [14063]. The last minor change
happened after 1.6.8 (6 -> 8), and MARSHAL_MAJOR was already 4 in v1_0_1,
7 years, 2 months ago (at which point I got tired of CVSweb).

Marshal's format is more stable than we think.

-- 
Mauricio Fernandez