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PERLTODO(1)	       Perl Programmers Reference Guide		   PERLTODO(1)

       perltodo - Perl TO-DO List

       This is a list of wishes for Perl. The most up to date version of this
       file is at

       The tasks we think are smaller or easier are listed first. Anyone is
       welcome to work on any of these, but it's a good idea to first contact to avoid duplication of effort, and to learn
       from any previous attempts. By all means contact a pumpking privately
       first if you prefer.

       Whilst patches to make the list shorter are most welcome, ideas to add
       to the list are also encouraged. Check the perl5-porters archives for
       past ideas, and any discussion about them. One set of archives may be
       found at:

       What can we offer you in return? Fame, fortune, and everlasting glory?
       Maybe not, but if your patch is incorporated, then we'll add your name
       to the AUTHORS file, which ships in the official distribution. How many
       other programming languages offer you 1 line of immortality?

Tasks that only need Perl knowledge
   Remove macperl references from tests
       MacPerl is gone. The tests don't need to be there.

   Remove duplication of test setup.
       Schwern notes, that there's duplication of code - lots and lots of
       tests have some variation on the big block of $Is_Foo checks.  We can
       safely put this into a file, change it to build an %Is hash and require
       it.  Maybe just put it into Throw in the handy tainting

   POD -> HTML conversion in the core still sucks
       Which is crazy given just how simple POD purports to be, and how simple
       HTML can be. It's not actually as simple as it sounds, particularly
       with the flexibility POD allows for "=item", but it would be good to
       improve the visual appeal of the HTML generated, and to avoid it having
       any validation errors. See also "make HTML install work", as the layout
       of installation tree is needed to improve the cross-linking.

       The addition of "Pod::Simple" and its related modules may make this
       task easier to complete.

   Make ExtUtils::ParseXS use strict;
       lib/ExtUtils/ contains this line

	   # use strict;  # One of these days...

       Simply uncomment it, and fix all the resulting issues :-)

       The more practical approach, to break the task down into manageable
       chunks, is to work your way though the code from bottom to top, or if
       necessary adding extra "{ ... }" blocks, and turning on strict within

   Parallel testing
       (This probably impacts much more than the core: also the Test::Harness
       and TAP::* modules on CPAN.)

       All of the tests in t/ can now be run in parallel, if $ENV{TEST_JOBS}
       is set. However, tests within each directory in ext and lib are still
       run in series, with directories run in parallel. This is an adequate
       heuristic, but it might be possible to relax it further, and get more
       throughput. Specifically, it would be good to audit all of lib/*.t, and
       make them use "File::Temp".

   Make Schwern poorer
       We should have tests for everything. When all the core's modules are
       tested, Schwern has promised to donate to $500 to TPF. We may need
       volunteers to hold him upside down and shake vigorously in order to
       actually extract the cash.

   Improve the coverage of the core tests
       Use Devel::Cover to ascertain the core modules's test coverage, then
       add tests that are currently missing.

   test B
       A full test suite for the B module would be nice.

   A decent benchmark
       "perlbench" seems impervious to any recent changes made to the perl
       core. It would be useful to have a reasonable general benchmarking
       suite that roughly represented what current perl programs do, and
       measurably reported whether tweaks to the core improve, degrade or
       don't really affect performance, to guide people attempting to optimise
       the guts of perl. Gisle would welcome new tests for perlbench.

   fix tainting bugs
       Fix the bugs revealed by running the test suite with the "-t" switch
       (via "make test.taintwarn").

   Dual life everything
       As part of the "dists" plan, anything that doesn't belong in the
       smallest perl distribution needs to be dual lifed. Anything else can be
       too. Figure out what changes would be needed to package that module and
       its tests up for CPAN, and do so. Test it with older perl releases, and
       fix the problems you find.

       To make a minimal perl distribution, it's useful to look at

   Bundle dual life modules in ext/
       For maintenance (and branch merging) reasons, it would be useful to
       move some architecture-independent dual-life modules from lib/ to ext/,
       if this has no negative impact on the build of perl itself.

   POSIX memory footprint
       Ilya observed that use POSIX; eats memory like there's no tomorrow, and
       at various times worked to cut it down. There is probably still fat to
       cut out - for example POSIX passes Exporter some very memory hungry
       data structures.
       There is a script that generates several header files to
       prefix all of Perl's symbols in a consistent way, to provide some
       semblance of namespace support in "C". Functions are declared in
       embed.fnc, variables in interpvar.h. Quite a few of the functions and
       variables are conditionally declared there, using "#ifdef". However, doesn't understand the C macros, so the rules about which
       symbols are present when is duplicated in Writing things
       twice is bad, m'kay.  It would be good to teach "" to
       understand the conditional compilation, and hence remove the
       duplication, and the mistakes it has caused.

   use strict; and AutoLoad
       Currently if you write

	   package Whack;
	   use AutoLoader 'AUTOLOAD';
	   use strict;
	   sub bloop {
	       print join (' ', No, strict, here), "!\n";

       then "use strict;" isn't in force within the autoloaded subroutines. It
       would be more consistent (and less surprising) to arrange for all
       lexical pragmas in force at the __END__ block to be in force within
       each autoloaded subroutine.

       There's a similar problem with SelfLoader.

   profile installman
       The installman script is slow. All it is doing text processing, which
       we're told is something Perl is good at. So it would be nice to know
       what it is doing that is taking so much CPU, and where possible address

Tasks that need a little sysadmin-type knowledge
       Or if you prefer, tasks that you would learn from, and broaden your
       skills base...

   make HTML install work
       There is an "installhtml" target in the Makefile. It's marked as
       "experimental". It would be good to get this tested, make it work
       reliably, and remove the "experimental" tag. This would include

       1.  Checking that cross linking between various parts of the
	   documentation works.	 In particular that links work between the
	   modules (files with POD in lib/) and the core documentation (files
	   in pod/)

       2.  Work out how to split "perlfunc" into chunks, preferably one per
	   function group, preferably with general case code that could be
	   used elsewhere.  Challenges here are correctly identifying the
	   groups of functions that go together, and making the right named
	   external cross-links point to the right page. Things to be aware of
	   are "-X", groups such as "getpwnam" to "endservent", two or more
	   "=items" giving the different parameter lists, such as

	       =item substr EXPR,OFFSET,LENGTH
	       =item substr EXPR,OFFSET

	   and different parameter lists having different meanings. (eg

   compressed man pages
       Be able to install them. This would probably need a configure test to
       see how the system does compressed man pages (same directory/different
       directory?  same filename/different filename), as well as tweaking the
       installman script to compress as necessary.

   Add a code coverage target to the Makefile
       Make it easy for anyone to run Devel::Cover on the core's tests. The
       steps to do this manually are roughly

       ·   do a normal "Configure", but include Devel::Cover as a module to
	   install (see INSTALL for how to do this)


	       make perl


	       cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness

       ·   Process the resulting Devel::Cover database

       This just give you the coverage of the .pms. To also get the C level
       coverage you need to

       ·   Additionally tell "Configure" to use the appropriate C compiler
	   flags for "gcov"


	       make perl.gcov

	   (instead of "make perl")

       ·   After running the tests run "gcov" to generate all the .gcov files.
	   (Including down in the subdirectories of ext/

       ·   (From the top level perl directory) run "gcov2perl" on all the
	   ".gcov" files to get their stats into the cover_db directory.

       ·   Then process the Devel::Cover database

       It would be good to add a single switch to "Configure" to specify that
       you wanted to perform perl level coverage, and another to specify C
       level coverage, and have "Configure" and the Makefile do all the right
       things automatically.

   Make cope with differences between built and installed perl
       Quite often vendors ship a perl binary compiled with their (pay-for)
       compilers.  People install a free compiler, such as gcc. To work out
       how to build extensions, Perl interrogates %Config, so in this
       situation %Config describes compilers that aren't there, and extension
       building fails. This forces people into choosing between re-compiling
       perl themselves using the compiler they have, or only using modules
       that the vendor ships.

       It would be good to find a way teach "" about the installation
       setup, possibly involving probing at install time or later, so that the
       %Config in a binary distribution better describes the installed
       machine, when the installed machine differs from the build machine in
       some significant way.

   linker specification files
       Some platforms mandate that you provide a list of a shared library's
       external symbols to the linker, so the core already has the
       infrastructure in place to do this for generating shared perl
       libraries. My understanding is that the GNU toolchain can accept an
       optional linker specification file, and restrict visibility just to
       symbols declared in that file. It would be good to extend to
       support this format, and to provide a means within "Configure" to
       enable it. This would allow Unix users to test that the export list is
       correct, and to build a perl that does not pollute the global namespace
       with private symbols.

   Cross-compile support
       Currently "Configure" understands "-Dusecrosscompile" option. This
       option arranges for building "miniperl" for TARGET machine, so this
       "miniperl" is assumed then to be copied to TARGET machine and used as a
       replacement of full "perl" executable.

       This could be done little differently. Namely "miniperl" should be
       built for HOST and then full "perl" with extensions should be compiled
       for TARGET.  This, however, might require extra trickery for %Config:
       we have one config first for HOST and then another for TARGET.  Tools
       like MakeMaker will be mightily confused.  Having around two different
       types of executables and libraries (HOST and TARGET) makes life
       interesting for Makefiles and shell (and Perl) scripts.	There is
       $Config{run}, normally empty, which can be used as an execution
       wrapper.	 Also note that in some cross-compilation/execution
       environments the HOST and the TARGET do not see the same filesystem(s),
       the $Config{run} may need to do some file/directory copying back and

       Make pod/roffitall be updated by pod/buildtoc.

   Split "linker" from "compiler"
       Right now, Configure probes for two commands, and sets two variables:

       ·   "cc" (in cc.U)

	   This variable holds the name of a command to execute a C compiler
	   which can resolve multiple global references that happen to have
	   the same name.  Usual values are cc and gcc.	 Fervent ANSI
	   compilers may be called c89.	 AIX has xlc.

       ·   "ld" (in dlsrc.U)

	   This variable indicates the program to be used to link libraries
	   for dynamic loading.	 On some systems, it is ld.  On ELF systems,
	   it should be $cc.  Mostly, we'll try to respect the hint file

       There is an implicit historical assumption from around Perl5.000alpha
       something, that $cc is also the correct command for linking object
       files together to make an executable. This may be true on Unix, but
       it's not true on other platforms, and there are a maze of work arounds
       in other places (such as Makefile.SH) to cope with this.

       Ideally, we should create a new variable to hold the name of the
       executable linker program, probe for it in Configure, and centralise
       all the special case logic there or in hints files.

       A small bikeshed issue remains - what to call it, given that $ld is
       already taken (arguably for the wrong thing now, but on SunOS 4.1 it is
       the command for creating dynamically-loadable modules) and $link could
       be confused with the Unix command line executable of the same name,
       which does something completely different. Andy Dougherty makes the
       counter argument "In parrot, I tried to call the command used to link
       object files and	 libraries into an executable link, since that's what
       my vaguely-remembered DOS and VMS experience suggested. I don't think
       any real confusion has ensued, so it's probably a reasonable name for
       perl5 to use."

       "Alas, I've always worried that introducing it would make things worse,
       since now the module building utilities would have to look for
       $Config{link} and institute a fall-back plan if it weren't found."
       Although I can see that as confusing, given that $Config{d_link} is
       true when (hard) links are available.

   Configure Windows using PowerShell
       Currently, Windows uses hard-coded config files based to build the
       config.h for compiling Perl.  Makefiles are also hard-coded and need to
       be hand edited prior to building Perl. While this makes it easy to
       create a perl.exe that works across multiple Windows versions, being
       able to accurately configure a perl.exe for a specific Windows versions
       and VS C++ would be a nice enhancement.	With PowerShell available on
       Windows XP and up, this may now be possible.  Step 1 might be to
       investigate whether this is possible and use this to clean up our
       current makefile situation.  Step 2 would be to see if there would be a
       way to use our existing metaconfig units to configure a Windows Perl or
       whether we go in a separate direction and make it so.  Of course, we
       all know what step 3 is.

   decouple -g and -DDEBUGGING
       Currently Configure automatically adds "-DDEBUGGING" to the C compiler
       flags if it spots "-g" in the optimiser flags. The pre-processor
       directive "DEBUGGING" enables perl's command line <-D> options, but in
       the process makes perl slower. It would be good to disentangle this
       logic, so that C-level debugging with "-g" and Perl level debugging
       with "-D" can easily be enabled independently.

Tasks that need a little C knowledge
       These tasks would need a little C knowledge, but don't need any
       specific background or experience with XS, or how the Perl interpreter

   Weed out needless PERL_UNUSED_ARG
       The C code uses the macro "PERL_UNUSED_ARG" to stop compilers warning
       about unused arguments. Often the arguments can't be removed, as there
       is an external constraint that determines the prototype of the
       function, so this approach is valid. However, there are some cases
       where "PERL_UNUSED_ARG" could be removed. Specifically

       ·   The prototypes of (nearly all) static functions can be changed

       ·   Unused arguments generated by short cut macros are wasteful - the
	   short cut macro used can be changed.

   Modernize the order of directories in @INC
       The way @INC is laid out by default, one cannot upgrade core (dual-
       life) modules without overwriting files. This causes problems for
       binary package builders.	 One possible proposal is laid out in this

       Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall.
       On these systems, it might be the default compilation mode, and there
       is currently no guarantee that passing no use64bitall option to the
       Configure process will build a 32bit perl. Implementing -Duse32bit*
       options would be nice for perl 5.12.

   Profile Perl - am I hot or not?
       The Perl source code is stable enough that it makes sense to profile
       it, identify and optimise the hotspots. It would be good to measure the
       performance of the Perl interpreter using free tools such as
       cachegrind, gprof, and dtrace, and work to reduce the bottlenecks they

       As part of this, the idea of pp_hot.c is that it contains the hot ops,
       the ops that are most commonly used. The idea is that by grouping them,
       their object code will be adjacent in the executable, so they have a
       greater chance of already being in the CPU cache (or swapped in) due to
       being near another op already in use.

       Except that it's not clear if these really are the most commonly used
       ops. So as part of exercising your skills with coverage and profiling
       tools you might want to determine what ops really are the most commonly
       used. And in turn suggest evictions and promotions to achieve a better

       One piece of Perl code that might make a good testbed is installman.

   Allocate OPs from arenas
       Currently all new OP structures are individually malloc()ed and
       free()d.	 All "malloc" implementations have space overheads, and are
       now as fast as custom allocates so it would both use less memory and
       less CPU to allocate the various OP structures from arenas. The SV
       arena code can probably be re-used for this.

       Note that Configuring perl with "-Accflags=-DPL_OP_SLAB_ALLOC" will use
       Perl_Slab_alloc() to pack optrees into a contiguous block, which is
       probably superior to the use of OP arenas, esp. from a cache locality
       standpoint.  See "Profile Perl - am I hot or not?".

   Improve win32/wince.c
       Currently, numerous functions look virtually, if not completely,
       identical in both "win32/wince.c" and "win32/win32.c" files, which
       can't be good.

   Use secure CRT functions when building with VC8 on Win32
       Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the
       basis that they were "unsafe" and introduced differently named secure
       versions of them as replacements, e.g. instead of writing

	   FILE* f = fopen(__FILE__, "r");

       one should now write

	   FILE* f;
	   errno_t err = fopen_s(&f, __FILE__, "r");

       Currently, the warnings about these deprecations have been disabled by
       adding -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to
       remove that warning suppressant and actually make use of the new secure
       CRT functions.

       There is also a similar issue with POSIX CRT function names like fileno
       having been deprecated in favour of ISO C++ conformant names like
       _fileno. These warnings are also currently suppressed by adding
       -D_CRT_NONSTDC_NO_DEPRECATE. It might be nice to do as Microsoft
       suggest here too, although, unlike the secure functions issue, there is
       presumably little or no benefit in this case.

   Fix POSIX::access() and chdir() on Win32
       These functions currently take no account of DACLs and therefore do not
       behave correctly in situations where access is restricted by DACLs (as
       opposed to the read-only attribute).

       Furthermore, POSIX::access() behaves differently for directories having
       the read-only attribute set depending on what CRT library is being
       used. For example, the _access() function in the VC6 and VC7 CRTs
       (wrongly) claim that such directories are not writable, whereas in fact
       all directories are writable unless access is denied by DACLs. (In the
       case of directories, the read-only attribute actually only means that
       the directory cannot be deleted.) This CRT bug is fixed in the VC8 and
       VC9 CRTs (but, of course, the directory may still not actually be
       writable if access is indeed denied by DACLs).

       For the chdir() issue, see ActiveState bug #74552:

       Therefore, DACLs should be checked both for consistency across CRTs and
       for the correct answer.

       (Note that perl's -w operator should not be modified to check DACLs. It
       has been written so that it reflects the state of the read-only
       attribute, even for directories (whatever CRT is being used), for
       symmetry with chmod().)

   strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
       Maybe create a utility that checks after each libperl.a creation that
       none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets()) ever
       creep back to libperl.a.

	 nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'

       Note, of course, that this will only tell whether your platform is
       using those naughty interfaces.

   -D_FORTIFY_SOURCE=2, -fstack-protector
       Recent glibcs support "-D_FORTIFY_SOURCE=2" and recent gcc (4.1
       onwards?) supports "-fstack-protector", both of which give protection
       against various kinds of buffer overflow problems.  These should
       probably be used for compiling Perl whenever available, Configure
       and/or hints files should be adjusted to probe for the availability of
       these features and enable them as appropriate.

   Arenas for GPs? For MAGIC?
       "struct gp" and "struct magic" are both currently allocated by
       "malloc".  It might be a speed or memory saving to change to using
       arenas. Or it might not. It would need some suitable benchmarking
       first. In particular, "GP"s can probably be changed with minimal
       compatibility impact (probably nothing outside of the core, or even
       outside of gv.c allocates them), but they probably aren't
       allocated/deallocated often enough for a speed saving. Whereas "MAGIC"
       is allocated/deallocated more often, but in turn, is also something
       more externally visible, so changing the rules here may bite external

   Shared arenas
       Several SV body structs are now the same size, notably PVMG and PVGV,
       PVAV and PVHV, and PVCV and PVFM. It should be possible to allocate and
       return same sized bodies from the same actual arena, rather than
       maintaining one arena for each. This could save 4-6K per thread, of
       memory no longer tied up in the not-yet-allocated part of an arena.

Tasks that need a knowledge of XS
       These tasks would need C knowledge, and roughly the level of knowledge
       of the perl API that comes from writing modules that use XS to
       interface to C.

   Remove the use of SVs as temporaries in dump.c
       dump.c contains debugging routines to dump out the contains of perl
       data structures, such as "SV"s, "AV"s and "HV"s. Currently, the dumping
       code uses "SV"s for its temporary buffers, which was a logical initial
       implementation choice, as they provide ready made memory handling.

       However, they also lead to a lot of confusion when it happens that what
       you're trying to debug is seen by the code in dump.c, correctly or
       incorrectly, as a temporary scalar it can use for a temporary buffer.
       It's also not possible to dump scalars before the interpreter is
       properly set up, such as during ithreads cloning. It would be good to
       progressively replace the use of scalars as string accumulation buffers
       with something much simpler, directly allocated by "malloc". The dump.c
       code is (or should be) only producing 7 bit US-ASCII, so output
       character sets are not an issue.

       Producing and proving an internal simple buffer allocation would make
       it easier to re-write the internals of the PerlIO subsystem to avoid
       using "SV"s for its buffers, use of which can cause problems similar to
       those of dump.c, at similar times.

   safely supporting POSIX SA_SIGINFO
       Some years ago Jarkko supplied patches to provide support for the POSIX
       SA_SIGINFO feature in Perl, passing the extra data to the Perl signal

       Unfortunately, it only works with "unsafe" signals, because under safe
       signals, by the time Perl gets to run the signal handler, the extra
       information has been lost. Moreover, it's not easy to store it
       somewhere, as you can't call mutexs, or do anything else fancy, from
       inside a signal handler.

       So it strikes me that we could provide safe SA_SIGINFO support

       1.  Provide global variables for two file descriptors

       2.  When the first request is made via "sigaction" for "SA_SIGINFO",
	   create a pipe, store the reader in one, the writer in the other

       3.  In the "safe" signal handler
	   ("Perl_csighandler()"/"S_raise_signal()"), if the "siginfo_t"
	   pointer non-"NULL", and the writer file handle is open,

	   1.	   serialise signal number, "struct siginfo_t" (or at least
		   the parts we care about) into a small auto char buff

	   2.	   "write()" that (non-blocking) to the writer fd

		   1.	       if it writes 100%, flag the signal in a counter
			       of "signals on the pipe" akin to the current
			       per-signal-number counts

		   2.	       if it writes 0%, assume the pipe is full. Flag
			       the data as lost?

		   3.	       if it writes partially, croak a panic, as your
			       OS is broken.

       4.  in the regular "PERL_ASYNC_CHECK()" processing, if there are
	   "signals on the pipe", read the data out, deserialise, build the
	   Perl structures on the stack (code in "Perl_sighandler()", the
	   "unsafe" handler), and call as usual.

       I think that this gets us decent "SA_SIGINFO" support, without the
       current risk of running Perl code inside the signal handler context.
       (With all the dangers of things like "malloc" corruption that that
       currently offers us)

       For more information see the thread starting with this message:

       Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no

       This task is incremental - even a little bit of work on it will help.

   Unicode in Filenames
       chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
       opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
       system, truncate, unlink, utime, -X.  All these could potentially
       accept Unicode filenames either as input or output (and in the case of
       system and qx Unicode in general, as input or output to/from the
       shell).	Whether a filesystem - an operating system pair understands
       Unicode in filenames varies.

       Known combinations that have some level of understanding include
       Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac OS
       X), NFS v4 is rumored to be Unicode, and of course Plan 9.  How to
       create Unicode filenames, what forms of Unicode are accepted and used
       (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
       and so on, varies.  Finding the right level of interfacing to Perl
       requires some thought.  Remember that an OS does not implicate a

       (The Windows -C command flag "wide API support" has been at least
       temporarily retired in 5.8.1, and the -C has been repurposed, see

       Most probably the right way to do this would be this: "Virtualize
       operating system access".

   Unicode in %ENV
       Currently the %ENV entries are always byte strings.  See "Virtualize
       operating system access".

   Unicode and glob()
       Currently glob patterns and filenames returned from File::Glob::glob()
       are always byte strings.	 See "Virtualize operating system access".

   Unicode and lc/uc operators
       Some built-in operators ("lc", "uc", etc.) behave differently, based on
       what the internal encoding of their argument is. That should not be the
       case. Maybe add a pragma to switch behaviour.

   use less 'memory'
       Investigate trade offs to switch out perl's choices on memory usage.
       Particularly perl should be able to give memory back.

       This task is incremental - even a little bit of work on it will help.

   Re-implement ":unique" in a way that is actually thread-safe
       The old implementation made bad assumptions on several levels. A good
       90% solution might be just to make ":unique" work to share the string
       buffer of SvPVs. That way large constant strings can be shared between
       ithreads, such as the configuration information in Config.

   Make tainting consistent
       Tainting would be easier to use if it didn't take documented shortcuts
       and allow taint to "leak" everywhere within an expression.

       system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
       running a shell. readpipe() (the function behind qx//) could be
       similarly extended.

   Audit the code for destruction ordering assumptions
       Change 25773 notes

	   /* Need to check SvMAGICAL, as during global destruction it may be that
	      AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
	      is now part of the linked list of SV heads, rather than pointing to
	      the original body.  */
	   /* FIXME - audit the code for other bugs like this one.  */

       adding the "SvMAGICAL" check to

	   if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
	       MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);

       Go through the core and look for similar assumptions that SVs have
       particular types, as all bets are off during global destruction.

   Extend PerlIO and PerlIO::Scalar
       PerlIO::Scalar doesn't know how to truncate().  Implementing this would
       require extending the PerlIO vtable.

       Similarly the PerlIO vtable doesn't know about formats (write()), or
       about stat(), or chmod()/chown(), utime(), or flock().

       (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership
       would mean.)

       PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(),
       opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(),

       See also "Virtualize operating system access".

   -C on the #! line
       It should be possible to make -C work correctly if found on the #!
       line, given that all perl command line options are strict ASCII, and -C
       changes only the interpretation of non-ASCII characters, and not for
       the script file handle. To make it work needs some investigation of the
       ordering of function calls during startup, and (by implication) a bit
       of tweaking of that order.

   Duplicate logic in S_method_common() and Perl_gv_fetchmethod_autoload()
       A comment in "S_method_common" notes

	       /* This code tries to figure out just what went wrong with
		  gv_fetchmethod.  It therefore needs to duplicate a lot of
		  the internals of that function.  We can't move it inside
		  Perl_gv_fetchmethod_autoload(), however, since that would
		  cause UNIVERSAL->can("NoSuchPackage::foo") to croak, and we
		  don't want that.

       If "Perl_gv_fetchmethod_autoload" gets rewritten to take (more) flag
       bits, then it ought to be possible to move the logic from
       "S_method_common" to the "right" place. When making this change it
       would probably be good to also pass in at least the method name length,
       if not also pre-computed hash values when known. (I'm contemplating a
       plan to pre-compute hash values for common fixed strings such as "ISA"
       and pass them in to functions.)

   Organize error messages
       Perl's diagnostics (error messages, see perldiag) could use
       reorganizing and formalizing so that each error message has its stable-
       for-all-eternity unique id, categorized by severity, type, and
       subsystem.  (The error messages would be listed in a datafile outside
       of the Perl source code, and the source code would only refer to the
       messages by the id.)  This clean-up and regularizing should apply for
       all croak() messages.

       This would enable all sorts of things: easier translation/localization
       of the messages (though please do keep in mind the caveats of
       Locale::Maketext about too straightforward approaches to translation),
       filtering by severity, and instead of grepping for a particular error
       message one could look for a stable error id.  (Of course, changing the
       error messages by default would break all the existing software
       depending on some particular error message...)

       This kind of functionality is known as message catalogs.	 Look for
       inspiration for example in the catgets() system, possibly even use it
       if available-- but only if available, all platforms will not have

       For the really pure at heart, consider extending this item to cover
       also the warning messages (see perllexwarn, "").

Tasks that need a knowledge of the interpreter
       These tasks would need C knowledge, and knowledge of how the
       interpreter works, or a willingness to learn.

   forbid labels with keyword names
       Currently "goto keyword" "computes" the label value:

	   $ perl -e 'goto print'
	   Can't find label 1 at -e line 1.

       It would be nice to forbid labels with keyword names, to avoid

   truncate() prototype
       The prototype of truncate() is currently $$. It should probably be "*$"
       instead. (This is changed in

   decapsulation of smart match argument
       Currently "$foo ~~ $object" will die with the message "Smart matching a
       non-overloaded object breaks encapsulation". It would be nice to allow
       to bypass this by using explictly the syntax "$foo ~~ %$object" or
       "$foo ~~ @$object".

   error reporting of [$a ; $b]
       Using ";" inside brackets is a syntax error, and we don't propose to
       change that by giving it any meaning. However, it's not reported very

	   $ perl -e '$a = [$b; $c];'
	   syntax error at -e line 1, near "$b;"
	   syntax error at -e line 1, near "$c]"
	   Execution of -e aborted due to compilation errors.

       It should be possible to hook into the tokeniser or the lexer, so that
       when a ";" is parsed where it is not legal as a statement terminator
       (ie inside "{}" used as a hashref, "[]" or "()") it issues an error
       something like ';' isn't legal inside an expression - if you need
       multiple statements use a do {...} block. See the thread starting at

   lexicals used only once
       This warns:

	   $ perl -we '$pie = 42'
	   Name "main::pie" used only once: possible typo at -e line 1.

       This does not:

	   $ perl -we 'my $pie = 42'

       Logically all lexicals used only once should warn, if the user asks for
       warnings.  An unworked RT ticket (#5087) has been open for almost seven
       years for this discrepancy.

   UTF-8 revamp
       The handling of Unicode is unclean in many places. For example, the
       regexp engine matches in Unicode semantics whenever the string or the
       pattern is flagged as UTF-8, but that should not be dependent on an
       internal storage detail of the string. Likewise, case folding behaviour
       is dependent on the UTF8 internal flag being on or off.

   Properly Unicode safe tokeniser and pads.
       The tokeniser isn't actually very UTF-8 clean. "use utf8;" is a hack -
       variable names are stored in stashes as raw bytes, without the utf-8
       flag set. The pad API only takes a "char *" pointer, so that's all
       bytes too. The tokeniser ignores the UTF-8-ness of "PL_rsfp", or any
       SVs returned from source filters.  All this could be fixed.

   state variable initialization in list context
       Currently this is illegal:

	   state ($a, $b) = foo();

       In Perl 6, "state ($a) = foo();" and "(state $a) = foo();" have
       different semantics, which is tricky to implement in Perl 5 as
       currently they produce the same opcode trees. The Perl 6 design is
       firm, so it would be good to implement the necessary code in Perl 5.
       There are comments in "Perl_newASSIGNOP()" that show the code paths
       taken by various assignment constructions involving state variables.

   Implement $value ~~ 0 .. $range
       It would be nice to extend the syntax of the "~~" operator to also
       understand numeric (and maybe alphanumeric) ranges.

   A does() built-in
       Like ref(), only useful. It would call the "DOES" method on objects; it
       would also tell whether something can be dereferenced as an
       array/hash/etc., or used as a regexp, etc.

   Tied filehandles and write() don't mix
       There is no method on tied filehandles to allow them to be called back
       by formats.

   Propagate compilation hints to the debugger
       Currently a debugger started with -dE on the command-line doesn't see
       the features enabled by -E. More generally hints ($^H and "%^H") aren't
       propagated to the debugger. Probably it would be a good thing to
       propagate hints from the innermost non-"DB::" scope: this would make
       code eval'ed in the debugger see the features (and strictures, etc.)
       currently in scope.

   Attach/detach debugger from running program
       The old perltodo notes "With "gdb", you can attach the debugger to a
       running program if you pass the process ID. It would be good to do this
       with the Perl debugger on a running Perl program, although I'm not sure
       how it would be done." ssh and screen do this with named pipes in /tmp.
       Maybe we can too.

   LVALUE functions for lists
       The old perltodo notes that lvalue functions don't work for list or
       hash slices. This would be good to fix.

   regexp optimiser optional
       The regexp optimiser is not optional. It should configurable to be, to
       allow its performance to be measured, and its bugs to be easily

   delete &function
       Allow to delete functions. One can already undef them, but they're
       still in the stash.

   "/w" regex modifier
       That flag would enable to match whole words, and also to interpolate
       arrays as alternations. With it, "/P/w" would be roughly equivalent to:

	   do { local $"='|'; /\b(?:P)\b/ }

       for the discussion.

   optional optimizer
       Make the peephole optimizer optional. Currently it performs two tasks
       as it walks the optree - genuine peephole optimisations, and necessary
       fixups of ops. It would be good to find an efficient way to switch out
       the optimisations whilst keeping the fixups.

   You WANT *how* many
       Currently contexts are void, scalar and list. split has a special
       mechanism in place to pass in the number of return values wanted. It
       would be useful to have a general mechanism for this, backwards
       compatible and little speed hit.	 This would allow proposals such as
       short circuiting sort to be implemented as a module on CPAN.

   lexical aliases
       Allow lexical aliases (maybe via the syntax "my \$alias = \$foo".

   entersub XS vs Perl
       At the moment pp_entersub is huge, and has code to deal with entering
       both perl and XS subroutines. Subroutine implementations rarely change
       between perl and XS at run time, so investigate using 2 ops to enter
       subs (one for XS, one for perl) and swap between if a sub is redefined.

       Self-ties are currently illegal because they caused too many segfaults.
       Maybe the causes of these could be tracked down and self-ties on all
       types reinstated.

   Optimize away @_
       The old perltodo notes "Look at the "reification" code in "av.c"".

   The yada yada yada operators
       Perl 6's Synopsis 3 says:

       The ... operator is the "yada, yada, yada" list operator, which is used
       as the body in function prototypes. It complains bitterly (by calling
       fail) if it is ever executed. Variant ??? calls warn, and !!! calls

       Those would be nice to add to Perl 5. That could be done without new

   Virtualize operating system access
       Implement a set of "vtables" that virtualizes operating system access
       (open(), mkdir(), unlink(), readdir(), getenv(), etc.)  At the very
       least these interfaces should take SVs as "name" arguments instead of
       bare char pointers; probably the most flexible and extensible way would
       be for the Perl-facing interfaces to accept HVs.	 The system needs to
       be per-operating-system and per-file-system hookable/filterable,
       preferably both from XS and Perl level ("Files and Filesystems" in
       perlport is good reading at this point, in fact, all of perlport is.)

       This has actually already been implemented (but only for Win32), take a
       look at iperlsys.h and win32/perlhost.h.	 While all Win32 variants go
       through a set of "vtables" for operating system access, non-Win32
       systems currently go straight for the POSIX/UNIX-style system/library
       call.  Similar system as for Win32 should be implemented for all
       platforms.  The existing Win32 implementation probably does not need to
       survive alongside this proposed new implementation, the approaches
       could be merged.

       What would this give us?	 One often-asked-for feature this would enable
       is using Unicode for filenames, and other "names" like %ENV, usernames,
       hostnames, and so forth.	 (See "When Unicode Does Not Happen" in

       But this kind of virtualization would also allow for things like
       virtual filesystems, virtual networks, and "sandboxes" (though as long
       as dynamic loading of random object code is allowed, not very safe
       sandboxes since external code of course know not of Perl's vtables).
       An example of a smaller "sandbox" is that this feature can be used to
       implement per-thread working directories: Win32 already does this.

       See also "Extend PerlIO and PerlIO::Scalar".

   Investigate PADTMP hash pessimisation
       The peephole optimiser converts constants used for hash key lookups to
       shared hash key scalars. Under ithreads, something is undoing this
       work.  See

   Store the current pad in the OP slab allocator
       Currently we leak ops in various cases of parse failure. I suggested
       that we could solve this by always using the op slab allocator, and
       walking it to free ops. Dave comments that as some ops are already
       freed during optree creation one would have to mark which ops are
       freed, and not double free them when walking the slab. He notes that
       one problem with this is that for some ops you have to know which pad
       was current at the time of allocation, which does change. I suggested
       storing a pointer to the current pad in the memory allocated for the
       slab, and swapping to a new slab each time the pad changes. Dave thinks
       that this would work.

   repack the optree
       Repacking the optree after execution order is determined could allow
       removal of NULL ops, and optimal ordering of OPs with respect to cache-
       line filling.  The slab allocator could be reused for this purpose.  I
       think that the best way to do this is to make it an optional step just
       before the completed optree is attached to anything else, and to use
       the slab allocator unchanged, so that freeing ops is identical whether
       or not this step runs.  Note that the slab allocator allocates ops
       downwards in memory, so one would have to actually "allocate" the ops
       in reverse-execution order to get them contiguous in memory in
       execution order.


       Note that running this copy, and then freeing all the old location ops
       would cause their slabs to be freed, which would eliminate possible
       memory wastage if the previous suggestion is implemented, and we swap
       slabs more frequently.

   eliminate incorrect line numbers in warnings
       This code

	   use warnings;
	   my $undef;

	   if ($undef == 3) {
	   } elsif ($undef == 0) {

       used to produce this output:

	   Use of uninitialized value in numeric eq (==) at line 4.
	   Use of uninitialized value in numeric eq (==) at line 4.

       where the line of the second warning was misreported - it should be
       line 5.	Rafael fixed this - the problem arose because there was no
       nextstate OP between the execution of the "if" and the "elsif", hence
       "PL_curcop" still reports that the currently executing line is line 4.
       The solution was to inject a nextstate OPs for each "elsif", although
       it turned out that the nextstate OP needed to be a nulled OP, rather
       than a live nextstate OP, else other line numbers became misreported.

       The problem is more general than "elsif" (although the "elsif" case is
       the most common and the most confusing). Ideally this code

	   use warnings;
	   my $undef;

	   my $a = $undef + 1;
	   my $b
	     = $undef
	     + 1;

       would produce this output

	   Use of uninitialized value $undef in addition (+) at line 4.
	   Use of uninitialized value $undef in addition (+) at line 7.

       (rather than lines 4 and 5), but this would seem to require every OP to
       carry (at least) line number information.

       What might work is to have an optional line number in memory just
       before the BASEOP structure, with a flag bit in the op to say whether
       it's present.  Initially during compile every OP would carry its line
       number. Then add a late pass to the optimiser (potentially combined
       with "repack the optree") which looks at the two ops on every edge of
       the graph of the execution path. If the line number changes, flags the
       destination OP with this information.  Once all paths are traced,
       replace every op with the flag with a nextstate-light op (that just
       updates "PL_curcop"), which in turn then passes control on to the true
       op. All ops would then be replaced by variants that do not store the
       line number. (Which, logically, why it would work best in conjunction
       with "repack the optree", as that is already copying/reallocating all
       the OPs)

       (Although I should note that we're not certain that doing this for the
       general case is worth it)

   optimize tail-calls
       Tail-calls present an opportunity for broadly applicable optimization;
       anywhere that "return foo(...)" is called, the outer return can be
       replaced by a goto, and foo will return directly to the outer caller,
       saving (conservatively) 25% of perl's call&return cost, which is
       relatively higher than in C.  The scheme language is known to do this
       heavily.	 B::Concise provides good insight into where this optimization
       is possible, ie anywhere entersub,leavesub op-sequence occurs.

	perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)'

       Bottom line on this is probably a new pp_tailcall function which
       combines the code in pp_entersub, pp_leavesub.  This should probably be
       done 1st in XS, and using B::Generate to patch the new OP into the

       It should be possible to add a "\N" regex assertion, meaning "every
       character except "\n"AX independently of the context. That would of
       course imply that "\N" couldn't be followed by an opening "{".

Big projects
       Tasks that will get your name mentioned in the description of the
       "Highlights of 5.12"

   make ithreads more robust
       Generally make ithreads more robust. See also "iCOW"

       This task is incremental - even a little bit of work on it will help,
       and will be greatly appreciated.

       One bit would be to write the missing code in sv.c:Perl_dirp_dup.

       Fix Perl_sv_dup, et al so that threads can return objects.

       Sarathy and Arthur have a proposal for an improved Copy On Write which
       specifically will be able to COW new ithreads. If this can be
       implemented it would be a good thing.

   (?{...}) closures in regexps
       Fix (or rewrite) the implementation of the "/(?{...})/" closures.

   A re-entrant regexp engine
       This will allow the use of a regex from inside (?{ }), (??{ }) and
       (?(?{ })|) constructs.

   Add class set operations to regexp engine
       Apparently these are quite useful. Anyway, Jeffery Friedl wants them.

       demerphq has this on his todo list, but right at the bottom.

Tasks for microperl
       [ Each and every one of these may be obsolete, but they were listed
	 in the old Todo.micro file]

   make creating automatic
   make creating Makefile.micro automatic
   do away with fork/exec/wait?
       (system, popen should be enough?)

   some of the really needs to be probed (using cc) in buildtime:
       (uConfigure? :-) native datatype widths and endianness come to mind

perl v5.10.1			  2009-08-10			   PERLTODO(1)

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