NAME

       PDL::IO::Dumper -- data dumping for structs with PDLs

DESCRIPTION

       This package allows you cleanly to save and restore complex data structures which include
       PDLs, as ASCII strings and/or transportable ASCII files.  It exports four functions into
       your namespace: sdump, fdump, frestore, and deep_copy.

       PDL::IO::Dumper traverses the same types of structure that Data::Dumper knows about,
       because it uses a call to Data::Dumper.  Unlike Data::Dumper it doesn't crash when
       accessing PDLs.

       The PDL::IO::Dumper routines have a slightly different syntax than Data::Dumper does: you
       may only dump a single scalar perl expression rather than an arbitrary one.  Of course,
       the scalar may be a ref to whatever humongous pile of spaghetti you want, so that's no big
       loss.

       The output string is intended to be about as readable as Dumper's output is for non-PDL
       expressions. To that end, small PDLs (up to 8 elements) are stored as inline perl
       expressions, midsized PDLs (up to 200 elements) are stored as perl expressions above the
       main data structure, and large PDLs are stored as FITS files that are uuencoded and
       included in the dump string. (You have to have access to either uuencode(1) or the CPAN
       module Convert::UU for this to work).

       No attempt is made to shrink the output string -- for example, inlined PDL expressions all
       include explicit reshape() and typecast commands, and uuencoding expands stuff by a factor
       of about 1.5.  So your data structures will grow when you dump them.

Bugs

       It's still possible to break this code and cause it to dump core, for the same reason that
       Data::Dumper crashes.  In particular, other external-hook variables aren't recognized (for
       that a more universal Dumper would be needed) and will still exercise the Data::Dumper
       crash.  This is by choice:  (A) it's difficult to recognize which objects are actually
       external, and (B) most everyday objects are quite safe.

       Another shortfall of Data::Dumper is that it doesn't recognize tied objects.  This might
       be a Good Thing or a Bad Thing depending on your point of view, but it means that
       PDL::IO::Dumper includes a kludge to handle the tied Astro::FITS::Header objects
       associated with FITS headers (see the rfits documentation in PDL::IO::Misc for details).

       There's currently no reference recursion detection, so a non-treelike reference topology
       will cause Dumper to buzz forever.  That will likely be fixed in a future version.
       Meanwhile a warning message finds likely cases.

Author, copyright, no warranty

       Copyright 2002, Craig DeForest.

       This code may be distributed under the same terms as Perl itself (license available at
       <http://ww.perl.org>).  Copying, reverse engineering, distribution, and modification are
       explicitly allowed so long as this notice is preserved intact and modified versions are
       clearly marked as such.

       This package comes with NO WARRANTY.

HISTORY

       •  1.0: initial release

       •  1.1 (26-Feb-2002): Shorter form for short PDLs; more readability

       •  1.2 (28-Feb-2002): Added deep_copy() -- exported convenience function
            for "eval sdump"

       •  1.3 (15-May-2002): Added checking for tied objects in gethdr()
            [workaround for hole in Data::Dumper]

       •  1.4 (15-Jan-2003): Added support for Convert::UU as well as
            command-line uu{en|de}code

FUNCTIONS

   sdump
       Dump a data structure to a string.

         use PDL::IO::Dumper;
         $s = sdump(<VAR>);
         ...
         <VAR> = eval $s;

       sdump dumps a single complex data structure into a string.  You restore the data structure
       by eval-ing the string.  Since eval is a builtin, no convenience routine exists to use it.

   fdump
       Dump a data structure to a file

         use PDL::IO::Dumper;
         fdump(<VAR>,$filename);
         ...
         <VAR> = frestore($filename);

       fdump dumps a single complex data structure to a file.  You restore the data structure by
       eval-ing the perl code put in the file.  A convenience routine (frestore) exists to do it
       for you.

       I suggest using the extension '.pld' or (for non-broken OS's) '.pdld' to distinguish
       Dumper files.  That way they are reminiscent of .pl files for perl, while still looking a
       little different so you can pick them out.  You can certainly feed a dump file straight
       into perl (for syntax checking) but it will not do much for you, just build your data
       structure and exit.

   frestore
       Restore a dumped file

         use PDL::IO::Dumper;
         fdump(<VAR>,$filename);
         ...
         <VAR> = frestore($filename);

       frestore() is a convenience function that just reads in the named file and executes it in
       an eval.  It's paired with fdump().

   deep_copy
       Convenience function copies a complete perl data structure by the brute force method of
       "eval sdump".

   PDL::IO::Dumper::big_PDL
       Identify whether a PDL is ``big'' [Internal routine]

       Internal routine takes a PDL and returns a boolean indicating whether it's small enough
       for direct insertion into the dump string.  If 0, it can be inserted.  Larger numbers
       yield larger scopes of PDL.  1 implies that it should be broken out but can be handled
       with a couple of perl commands; 2 implies full uudecode treatment.

       PDLs with Astro::FITS::Header objects as headers are taken to be FITS files and are always
       treated as huge, regardless of size.

   PDL::IO::Dumper::stringify_PDL
       Turn a PDL into a 1-part perl expr [Internal routine]

       Internal routine that takes a PDL and returns a perl string that evals to the PDL.  It
       should be used with care because it doesn't dump headers and it doesn't check number of
       elements.  The point here is that numbers are dumped with the correct precision for their
       storage class.  Things we don't know about get stringified element-by-element by their
       builtin class, which is probably not a bad guess.

   PDL::IO::Dumper::uudecode_PDL
       Recover a PDL from a uuencoded string [Internal routine]

       This routine encapsulates uudecoding of the dumped string for large piddles.  It's
       separate to encapsulate the decision about which method of uudecoding to try (both the
       built-in Convert::UU and the shell command uudecode(1) are supported).

   PDL::IO::Dumper::dump_PDL
       Generate 1- or 2-part expr for a PDL [Internal routine]

       Internal routine that produces commands defining a PDL.  You supply (<PDL>, <name>) and
       get back two strings: a prepended command string and an expr that evaluates to the final
       PDL.  PDL is the PDL you want to dump.  <inline> is a flag whether dump_PDL is being
       called inline or before the inline dump string (0 for before; 1 for in).  <name> is the
       name of the variable to be assigned (for medium and large PDLs, which are defined before
       the dump string and assigned unique IDs).

   PDL::IO::Dumper::find_PDLs
       Walk a data structure and dump PDLs [Internal routine]

       Walks the original data structure and generates appropriate exprs for each PDL.  The exprs
       are inserted into the Data::Dumper output string.  You shouldn't call this unless you know
       what you're doing.  (see sdump, above).