3 perltodo - Perl TO-DO List
7 This is a list of wishes for Perl. The tasks we think are smaller or easier
8 are listed first. Anyone is welcome to work on any of these, but it's a good
9 idea to first contact I<perl5-porters@perl.org> to avoid duplication of
10 effort. By all means contact a pumpking privately first if you prefer.
12 Whilst patches to make the list shorter are most welcome, ideas to add to
13 the list are also encouraged. Check the perl5-porters archives for past
14 ideas, and any discussion about them. One set of archives may be found at:
16 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
18 What can we offer you in return? Fame, fortune, and everlasting glory? Maybe
19 not, but if your patch is incorporated, then we'll add your name to the
20 F<AUTHORS> file, which ships in the official distribution. How many other
21 programming languages offer you 1 line of immortality?
23 =head1 Tasks that only need Perl knowledge
25 =head2 Remove duplication of test setup.
27 Schwern notes, that there's duplication of code - lots and lots of tests have
28 some variation on the big block of C<$Is_Foo> checks. We can safely put this
29 into a file, change it to build an C<%Is> hash and require it. Maybe just put
30 it into F<test.pl>. Throw in the handy tainting subroutines.
32 =head2 merge common code in installperl and installman
34 There are some common subroutines and a common C<BEGIN> block in F<installperl>
35 and F<installman>. These should probably be merged. It would also be good to
36 check for duplication in all the utility scripts supplied in the source
37 tarball. It might be good to move them all to a subdirectory, but this would
38 require careful checking to find all places that call them, and change those
41 =head2 common test code for timed bail out
43 Write portable self destruct code for tests to stop them burning CPU in
44 infinite loops. This needs to avoid using alarm, as some of the tests are
45 testing alarm/sleep or timers.
47 =head2 POD -E<gt> HTML conversion in the core still sucks
49 Which is crazy given just how simple POD purports to be, and how simple HTML
50 can be. It's not actually I<as> simple as it sounds, particularly with the
51 flexibility POD allows for C<=item>, but it would be good to improve the
52 visual appeal of the HTML generated, and to avoid it having any validation
53 errors. See also L</make HTML install work>, as the layout of installation tree
54 is needed to improve the cross-linking.
56 The addition of C<Pod::Simple> and its related modules may make this task
59 =head2 merge checkpods and podchecker
61 F<pod/checkpods.PL> (and C<make check> in the F<pod/> subdirectory)
62 implements a very basic check for pod files, but the errors it discovers
63 aren't found by podchecker. Add this check to podchecker, get rid of
64 checkpods and have C<make check> use podchecker.
66 =head2 perlmodlib.PL rewrite
68 Currently perlmodlib.PL needs to be run from a source directory where perl
69 has been built, or some modules won't be found, and others will be
70 skipped. Make it run from a clean perl source tree (so it's reproducible).
72 =head2 Parallel testing
74 (This probably impacts much more than the core: also the Test::Harness
75 and TAP::* modules on CPAN.)
77 The core regression test suite is getting ever more comprehensive, which has
78 the side effect that it takes longer to run. This isn't so good. Investigate
79 whether it would be feasible to give the harness script the B<option> of
80 running sets of tests in parallel. This would be useful for tests in
81 F<t/op/*.t> and F<t/uni/*.t> and maybe some sets of tests in F<lib/>.
89 How does screen layout work when you're running more than one test?
93 How does the caller of test specify how many tests to run in parallel?
97 How do setup/teardown tests identify themselves?
101 Pugs already does parallel testing - can their approach be re-used?
103 =head2 Make Schwern poorer
105 We should have tests for everything. When all the core's modules are tested,
106 Schwern has promised to donate to $500 to TPF. We may need volunteers to
107 hold him upside down and shake vigorously in order to actually extract the
110 =head2 Improve the coverage of the core tests
112 Use Devel::Cover to ascertain the core modules's test coverage, then add
113 tests that are currently missing.
117 A full test suite for the B module would be nice.
119 =head2 Deparse inlined constants
123 use constant PI => 4;
126 will currently deparse as
128 use constant ('PI', 4);
131 because the tokenizer inlines the value of the constant subroutine C<PI>.
132 This allows various compile time optimisations, such as constant folding
133 and dead code elimination. Where these haven't happened (such as the example
134 above) it ought be possible to make B::Deparse work out the name of the
135 original constant, because just enough information survives in the symbol
136 table to do this. Specifically, the same scalar is used for the constant in
137 the optree as is used for the constant subroutine, so by iterating over all
138 symbol tables and generating a mapping of SV address to constant name, it
139 would be possible to provide B::Deparse with this functionality.
141 =head2 A decent benchmark
143 C<perlbench> seems impervious to any recent changes made to the perl core. It
144 would be useful to have a reasonable general benchmarking suite that roughly
145 represented what current perl programs do, and measurably reported whether
146 tweaks to the core improve, degrade or don't really affect performance, to
147 guide people attempting to optimise the guts of perl. Gisle would welcome
148 new tests for perlbench.
150 =head2 fix tainting bugs
152 Fix the bugs revealed by running the test suite with the C<-t> switch (via
153 C<make test.taintwarn>).
155 =head2 Dual life everything
157 As part of the "dists" plan, anything that doesn't belong in the smallest perl
158 distribution needs to be dual lifed. Anything else can be too. Figure out what
159 changes would be needed to package that module and its tests up for CPAN, and
160 do so. Test it with older perl releases, and fix the problems you find.
162 To make a minimal perl distribution, it's useful to look at
163 F<t/lib/commonsense.t>.
165 =head2 Improving C<threads::shared>
167 Investigate whether C<threads::shared> could share aggregates properly with
168 only Perl level changes to shared.pm
170 =head2 POSIX memory footprint
172 Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
173 various times worked to cut it down. There is probably still fat to cut out -
174 for example POSIX passes Exporter some very memory hungry data structures.
176 =head2 embed.pl/makedef.pl
178 There is a script F<embed.pl> that generates several header files to prefix
179 all of Perl's symbols in a consistent way, to provide some semblance of
180 namespace support in C<C>. Functions are declared in F<embed.fnc>, variables
181 in F<interpvar.h>. Quite a few of the functions and variables
182 are conditionally declared there, using C<#ifdef>. However, F<embed.pl>
183 doesn't understand the C macros, so the rules about which symbols are present
184 when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay.
185 It would be good to teach C<embed.pl> to understand the conditional
186 compilation, and hence remove the duplication, and the mistakes it has caused.
188 =head2 use strict; and AutoLoad
190 Currently if you write
193 use AutoLoader 'AUTOLOAD';
198 print join (' ', No, strict, here), "!\n";
201 then C<use strict;> isn't in force within the autoloaded subroutines. It would
202 be more consistent (and less surprising) to arrange for all lexical pragmas
203 in force at the __END__ block to be in force within each autoloaded subroutine.
205 There's a similar problem with SelfLoader.
207 =head1 Tasks that need a little sysadmin-type knowledge
209 Or if you prefer, tasks that you would learn from, and broaden your skills
212 =head2 make HTML install work
214 There is an C<installhtml> target in the Makefile. It's marked as
215 "experimental". It would be good to get this tested, make it work reliably, and
216 remove the "experimental" tag. This would include
222 Checking that cross linking between various parts of the documentation works.
223 In particular that links work between the modules (files with POD in F<lib/>)
224 and the core documentation (files in F<pod/>)
228 Work out how to split C<perlfunc> into chunks, preferably one per function
229 group, preferably with general case code that could be used elsewhere.
230 Challenges here are correctly identifying the groups of functions that go
231 together, and making the right named external cross-links point to the right
232 page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
233 C<endservent>, two or more C<=items> giving the different parameter lists, such
236 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
237 =item substr EXPR,OFFSET,LENGTH
238 =item substr EXPR,OFFSET
240 and different parameter lists having different meanings. (eg C<select>)
244 =head2 compressed man pages
246 Be able to install them. This would probably need a configure test to see how
247 the system does compressed man pages (same directory/different directory?
248 same filename/different filename), as well as tweaking the F<installman> script
249 to compress as necessary.
251 =head2 Add a code coverage target to the Makefile
253 Make it easy for anyone to run Devel::Cover on the core's tests. The steps
254 to do this manually are roughly
260 do a normal C<Configure>, but include Devel::Cover as a module to install
261 (see F<INSTALL> for how to do this)
269 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
273 Process the resulting Devel::Cover database
277 This just give you the coverage of the F<.pm>s. To also get the C level
284 Additionally tell C<Configure> to use the appropriate C compiler flags for
291 (instead of C<make perl>)
295 After running the tests run C<gcov> to generate all the F<.gcov> files.
296 (Including down in the subdirectories of F<ext/>
300 (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
301 to get their stats into the cover_db directory.
305 Then process the Devel::Cover database
309 It would be good to add a single switch to C<Configure> to specify that you
310 wanted to perform perl level coverage, and another to specify C level
311 coverage, and have C<Configure> and the F<Makefile> do all the right things
314 =head2 Make Config.pm cope with differences between built and installed perl
316 Quite often vendors ship a perl binary compiled with their (pay-for)
317 compilers. People install a free compiler, such as gcc. To work out how to
318 build extensions, Perl interrogates C<%Config>, so in this situation
319 C<%Config> describes compilers that aren't there, and extension building
320 fails. This forces people into choosing between re-compiling perl themselves
321 using the compiler they have, or only using modules that the vendor ships.
323 It would be good to find a way teach C<Config.pm> about the installation setup,
324 possibly involving probing at install time or later, so that the C<%Config> in
325 a binary distribution better describes the installed machine, when the
326 installed machine differs from the build machine in some significant way.
328 =head2 linker specification files
330 Some platforms mandate that you provide a list of a shared library's external
331 symbols to the linker, so the core already has the infrastructure in place to
332 do this for generating shared perl libraries. My understanding is that the
333 GNU toolchain can accept an optional linker specification file, and restrict
334 visibility just to symbols declared in that file. It would be good to extend
335 F<makedef.pl> to support this format, and to provide a means within
336 C<Configure> to enable it. This would allow Unix users to test that the
337 export list is correct, and to build a perl that does not pollute the global
338 namespace with private symbols.
340 =head2 Cross-compile support
342 Currently C<Configure> understands C<-Dusecrosscompile> option. This option
343 arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is
344 assumed then to be copied to TARGET machine and used as a replacement of full
347 This could be done little differently. Namely C<miniperl> should be built for
348 HOST and then full C<perl> with extensions should be compiled for TARGET.
349 This, however, might require extra trickery for %Config: we have one config
350 first for HOST and then another for TARGET. Tools like MakeMaker will be
351 mightily confused. Having around two different types of executables and
352 libraries (HOST and TARGET) makes life interesting for Makefiles and
353 shell (and Perl) scripts. There is $Config{run}, normally empty, which
354 can be used as an execution wrapper. Also note that in some
355 cross-compilation/execution environments the HOST and the TARGET do
356 not see the same filesystem(s), the $Config{run} may need to do some
357 file/directory copying back and forth.
361 Make F<pod/roffitall> be updated by F<pod/buildtoc>.
363 =head1 Tasks that need a little C knowledge
365 These tasks would need a little C knowledge, but don't need any specific
366 background or experience with XS, or how the Perl interpreter works
368 =head2 Weed out needless PERL_UNUSED_ARG
370 The C code uses the macro C<PERL_UNUSED_ARG> to stop compilers warning about
371 unused arguments. Often the arguments can't be removed, as there is an
372 external constraint that determines the prototype of the function, so this
373 approach is valid. However, there are some cases where C<PERL_UNUSED_ARG>
374 could be removed. Specifically
380 The prototypes of (nearly all) static functions can be changed
384 Unused arguments generated by short cut macros are wasteful - the short cut
385 macro used can be changed.
389 =head2 Modernize the order of directories in @INC
391 The way @INC is laid out by default, one cannot upgrade core (dual-life)
392 modules without overwriting files. This causes problems for binary
393 package builders. One possible proposal is laid out in this
395 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html>.
399 Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall.
400 On these systems, it might be the default compilation mode, and there
401 is currently no guarantee that passing no use64bitall option to the
402 Configure process will build a 32bit perl. Implementing -Duse32bit*
403 options would be nice for perl 5.12.
405 =head2 Make it clear from -v if this is the exact official release
407 Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
408 usually defines one local patch, of the form "MAINT12345" or "RC1". The output
409 of perl -v doesn't report that a perl isn't an official release, and this
410 information can get lost in bugs reports. Because of this, the minor version
411 isn't bumped up until RC time, to minimise the possibility of versions of perl
412 escaping that believe themselves to be newer than they actually are.
414 It would be useful to find an elegant way to have the "this is an interim
415 maintenance release" or "this is a release candidate" in the terse -v output,
416 and have it so that it's easy for the pumpking to remove this just as the
417 release tarball is rolled up. This way the version pulled out of rsync would
418 always say "I'm a development release" and it would be safe to bump the
419 reported minor version as soon as a release ships, which would aid perl
422 This task is really about thinking of an elegant way to arrange the C source
423 such that it's trivial for the Pumpking to flag "this is an official release"
424 when making a tarball, yet leave the default source saying "I'm not the
427 =head2 Profile Perl - am I hot or not?
429 The Perl source code is stable enough that it makes sense to profile it,
430 identify and optimise the hotspots. It would be good to measure the
431 performance of the Perl interpreter using free tools such as cachegrind,
432 gprof, and dtrace, and work to reduce the bottlenecks they reveal.
434 As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
435 the ops that are most commonly used. The idea is that by grouping them, their
436 object code will be adjacent in the executable, so they have a greater chance
437 of already being in the CPU cache (or swapped in) due to being near another op
440 Except that it's not clear if these really are the most commonly used ops. So
441 as part of exercising your skills with coverage and profiling tools you might
442 want to determine what ops I<really> are the most commonly used. And in turn
443 suggest evictions and promotions to achieve a better F<pp_hot.c>.
445 =head2 Allocate OPs from arenas
447 Currently all new OP structures are individually malloc()ed and free()d.
448 All C<malloc> implementations have space overheads, and are now as fast as
449 custom allocates so it would both use less memory and less CPU to allocate
450 the various OP structures from arenas. The SV arena code can probably be
453 Note that Configuring perl with C<-Accflags=-DPL_OP_SLAB_ALLOC> will use
454 Perl_Slab_alloc() to pack optrees into a contiguous block, which is
455 probably superior to the use of OP arenas, esp. from a cache locality
456 standpoint. See L<Profile Perl - am I hot or not?>.
458 =head2 Improve win32/wince.c
460 Currently, numerous functions look virtually, if not completely,
461 identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't
464 =head2 Use secure CRT functions when building with VC8 on Win32
466 Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis
467 that they were "unsafe" and introduced differently named secure versions of
468 them as replacements, e.g. instead of writing
470 FILE* f = fopen(__FILE__, "r");
475 errno_t err = fopen_s(&f, __FILE__, "r");
477 Currently, the warnings about these deprecations have been disabled by adding
478 -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that
479 warning suppressant and actually make use of the new secure CRT functions.
481 There is also a similar issue with POSIX CRT function names like fileno having
482 been deprecated in favour of ISO C++ conformant names like _fileno. These
483 warnings are also currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It
484 might be nice to do as Microsoft suggest here too, although, unlike the secure
485 functions issue, there is presumably little or no benefit in this case.
487 =head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
489 Maybe create a utility that checks after each libperl.a creation that
490 none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets())
491 ever creep back to libperl.a.
493 nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'
495 Note, of course, that this will only tell whether B<your> platform
496 is using those naughty interfaces.
498 =head2 -D_FORTIFY_SOURCE=2, -fstack-protector
500 Recent glibcs support C<-D_FORTIFY_SOURCE=2> and recent gcc
501 (4.1 onwards?) supports C<-fstack-protector>, both of which give
502 protection against various kinds of buffer overflow problems.
503 These should probably be used for compiling Perl whenever available,
504 Configure and/or hints files should be adjusted to probe for the
505 availability of these features and enable them as appropriate.
507 =head2 Arenas for GPs? For MAGIC?
509 C<struct gp> and C<struct magic> are both currently allocated by C<malloc>.
510 It might be a speed or memory saving to change to using arenas. Or it might
511 not. It would need some suitable benchmarking first. In particular, C<GP>s
512 can probably be changed with minimal compatibility impact (probably nothing
513 outside of the core, or even outside of F<gv.c> allocates them), but they
514 probably aren't allocated/deallocated often enough for a speed saving. Whereas
515 C<MAGIC> is allocated/deallocated more often, but in turn, is also something
516 more externally visible, so changing the rules here may bite external code.
519 =head1 Tasks that need a knowledge of XS
521 These tasks would need C knowledge, and roughly the level of knowledge of
522 the perl API that comes from writing modules that use XS to interface to
525 =head2 autovivification
527 Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
529 This task is incremental - even a little bit of work on it will help.
531 =head2 Unicode in Filenames
533 chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
534 opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
535 system, truncate, unlink, utime, -X. All these could potentially accept
536 Unicode filenames either as input or output (and in the case of system
537 and qx Unicode in general, as input or output to/from the shell).
538 Whether a filesystem - an operating system pair understands Unicode in
541 Known combinations that have some level of understanding include
542 Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
543 OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
544 create Unicode filenames, what forms of Unicode are accepted and used
545 (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
546 and so on, varies. Finding the right level of interfacing to Perl
547 requires some thought. Remember that an OS does not implicate a
550 (The Windows -C command flag "wide API support" has been at least
551 temporarily retired in 5.8.1, and the -C has been repurposed, see
554 Most probably the right way to do this would be this:
555 L</"Virtualize operating system access">.
557 =head2 Unicode in %ENV
559 Currently the %ENV entries are always byte strings.
560 See L</"Virtualize operating system access">.
562 =head2 Unicode and glob()
564 Currently glob patterns and filenames returned from File::Glob::glob()
565 are always byte strings. See L</"Virtualize operating system access">.
567 =head2 Unicode and lc/uc operators
569 Some built-in operators (C<lc>, C<uc>, etc.) behave differently, based on
570 what the internal encoding of their argument is. That should not be the
571 case. Maybe add a pragma to switch behaviour.
573 =head2 use less 'memory'
575 Investigate trade offs to switch out perl's choices on memory usage.
576 Particularly perl should be able to give memory back.
578 This task is incremental - even a little bit of work on it will help.
580 =head2 Re-implement C<:unique> in a way that is actually thread-safe
582 The old implementation made bad assumptions on several levels. A good 90%
583 solution might be just to make C<:unique> work to share the string buffer
584 of SvPVs. That way large constant strings can be shared between ithreads,
585 such as the configuration information in F<Config>.
587 =head2 Make tainting consistent
589 Tainting would be easier to use if it didn't take documented shortcuts and
590 allow taint to "leak" everywhere within an expression.
592 =head2 readpipe(LIST)
594 system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
595 running a shell. readpipe() (the function behind qx//) could be similarly
598 =head2 Audit the code for destruction ordering assumptions
602 /* Need to check SvMAGICAL, as during global destruction it may be that
603 AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
604 is now part of the linked list of SV heads, rather than pointing to
605 the original body. */
606 /* FIXME - audit the code for other bugs like this one. */
608 adding the C<SvMAGICAL> check to
610 if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
611 MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);
613 Go through the core and look for similar assumptions that SVs have particular
614 types, as all bets are off during global destruction.
616 =head2 Extend PerlIO and PerlIO::Scalar
618 PerlIO::Scalar doesn't know how to truncate(). Implementing this
619 would require extending the PerlIO vtable.
621 Similarly the PerlIO vtable doesn't know about formats (write()), or
622 about stat(), or chmod()/chown(), utime(), or flock().
624 (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership
627 PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(),
628 opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(),
631 See also L</"Virtualize operating system access">.
633 =head2 -C on the #! line
635 It should be possible to make -C work correctly if found on the #! line,
636 given that all perl command line options are strict ASCII, and -C changes
637 only the interpretation of non-ASCII characters, and not for the script file
638 handle. To make it work needs some investigation of the ordering of function
639 calls during startup, and (by implication) a bit of tweaking of that order.
641 =head2 Propagate const outwards from Perl_moreswitches()
643 Change 32057 changed the parameter and return value of C<Perl_moreswitches()>
644 from <char *> to <const char *>. It should now be possible to propagate
645 const-correctness outwards to C<S_parse_body()>, C<Perl_moreswitches()>
648 =head2 Duplicate logic in S_method_common() and Perl_gv_fetchmethod_autoload()
650 A comment in C<S_method_common> notes
652 /* This code tries to figure out just what went wrong with
653 gv_fetchmethod. It therefore needs to duplicate a lot of
654 the internals of that function. We can't move it inside
655 Perl_gv_fetchmethod_autoload(), however, since that would
656 cause UNIVERSAL->can("NoSuchPackage::foo") to croak, and we
660 If C<Perl_gv_fetchmethod_autoload> gets rewritten to take (more) flag bits,
661 then it ought to be possible to move the logic from C<S_method_common> to
662 the "right" place. When making this change it would probably be good to also
663 pass in at least the method name length, if not also pre-computed hash values
664 when known. (I'm contemplating a plan to pre-compute hash values for common
665 fixed strings such as C<ISA> and pass them in to functions.)
667 =head2 Organize error messages
669 Perl's diagnostics (error messages, see L<perldiag>) could use
670 reorganizing and formalizing so that each error message has its
671 stable-for-all-eternity unique id, categorized by severity, type, and
672 subsystem. (The error messages would be listed in a datafile outside
673 of the Perl source code, and the source code would only refer to the
674 messages by the id.) This clean-up and regularizing should apply
675 for all croak() messages.
677 This would enable all sorts of things: easier translation/localization
678 of the messages (though please do keep in mind the caveats of
679 L<Locale::Maketext> about too straightforward approaches to
680 translation), filtering by severity, and instead of grepping for a
681 particular error message one could look for a stable error id. (Of
682 course, changing the error messages by default would break all the
683 existing software depending on some particular error message...)
685 This kind of functionality is known as I<message catalogs>. Look for
686 inspiration for example in the catgets() system, possibly even use it
687 if available-- but B<only> if available, all platforms will B<not>
690 For the really pure at heart, consider extending this item to cover
691 also the warning messages (see L<perllexwarn>, C<warnings.pl>).
693 =head1 Tasks that need a knowledge of the interpreter
695 These tasks would need C knowledge, and knowledge of how the interpreter works,
696 or a willingness to learn.
698 =head2 lexicals used only once
702 $ perl -we '$pie = 42'
703 Name "main::pie" used only once: possible typo at -e line 1.
707 $ perl -we 'my $pie = 42'
709 Logically all lexicals used only once should warn, if the user asks for
710 warnings. An unworked RT ticket (#5087) has been open for almost seven
711 years for this discrepancy.
715 The handling of Unicode is unclean in many places. For example, the regexp
716 engine matches in Unicode semantics whenever the string or the pattern is
717 flagged as UTF-8, but that should not be dependent on an internal storage
718 detail of the string. Likewise, case folding behaviour is dependent on the
719 UTF8 internal flag being on or off.
721 =head2 Properly Unicode safe tokeniser and pads.
723 The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
724 variable names are stored in stashes as raw bytes, without the utf-8 flag
725 set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
726 tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
727 source filters. All this could be fixed.
729 =head2 state variable initialization in list context
731 Currently this is illegal:
733 state ($a, $b) = foo();
735 In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different
736 semantics, which is tricky to implement in Perl 5 as currently they produce
737 the same opcode trees. The Perl 6 design is firm, so it would be good to
738 implement the necessary code in Perl 5. There are comments in
739 C<Perl_newASSIGNOP()> that show the code paths taken by various assignment
740 constructions involving state variables.
742 =head2 Implement $value ~~ 0 .. $range
744 It would be nice to extend the syntax of the C<~~> operator to also
745 understand numeric (and maybe alphanumeric) ranges.
747 =head2 A does() built-in
749 Like ref(), only useful. It would call the C<DOES> method on objects; it
750 would also tell whether something can be dereferenced as an
751 array/hash/etc., or used as a regexp, etc.
752 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html>
754 =head2 Tied filehandles and write() don't mix
756 There is no method on tied filehandles to allow them to be called back by
759 =head2 Attach/detach debugger from running program
761 The old perltodo notes "With C<gdb>, you can attach the debugger to a running
762 program if you pass the process ID. It would be good to do this with the Perl
763 debugger on a running Perl program, although I'm not sure how it would be
764 done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
766 =head2 Optimize away empty destructors
768 Defining an empty DESTROY method might be useful (notably in
769 AUTOLOAD-enabled classes), but it's still a bit expensive to call. That
770 could probably be optimized.
772 =head2 LVALUE functions for lists
774 The old perltodo notes that lvalue functions don't work for list or hash
775 slices. This would be good to fix.
777 =head2 LVALUE functions in the debugger
779 The old perltodo notes that lvalue functions don't work in the debugger. This
780 would be good to fix.
782 =head2 regexp optimiser optional
784 The regexp optimiser is not optional. It should configurable to be, to allow
785 its performance to be measured, and its bugs to be easily demonstrated.
787 =head2 delete &function
789 Allow to delete functions. One can already undef them, but they're still
792 =head2 C</w> regex modifier
794 That flag would enable to match whole words, and also to interpolate
795 arrays as alternations. With it, C</P/w> would be roughly equivalent to:
797 do { local $"='|'; /\b(?:P)\b/ }
799 See L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html>
802 =head2 optional optimizer
804 Make the peephole optimizer optional. Currently it performs two tasks as
805 it walks the optree - genuine peephole optimisations, and necessary fixups of
806 ops. It would be good to find an efficient way to switch out the
807 optimisations whilst keeping the fixups.
809 =head2 You WANT *how* many
811 Currently contexts are void, scalar and list. split has a special mechanism in
812 place to pass in the number of return values wanted. It would be useful to
813 have a general mechanism for this, backwards compatible and little speed hit.
814 This would allow proposals such as short circuiting sort to be implemented
817 =head2 lexical aliases
819 Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
821 =head2 entersub XS vs Perl
823 At the moment pp_entersub is huge, and has code to deal with entering both
824 perl and XS subroutines. Subroutine implementations rarely change between
825 perl and XS at run time, so investigate using 2 ops to enter subs (one for
826 XS, one for perl) and swap between if a sub is redefined.
830 Self-ties are currently illegal because they caused too many segfaults. Maybe
831 the causes of these could be tracked down and self-ties on all types
834 =head2 Optimize away @_
836 The old perltodo notes "Look at the "reification" code in C<av.c>".
838 =head2 The yada yada yada operators
840 Perl 6's Synopsis 3 says:
842 I<The ... operator is the "yada, yada, yada" list operator, which is used as
843 the body in function prototypes. It complains bitterly (by calling fail)
844 if it is ever executed. Variant ??? calls warn, and !!! calls die.>
846 Those would be nice to add to Perl 5. That could be done without new ops.
848 =head2 Virtualize operating system access
850 Implement a set of "vtables" that virtualizes operating system access
851 (open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very
852 least these interfaces should take SVs as "name" arguments instead of
853 bare char pointers; probably the most flexible and extensible way
854 would be for the Perl-facing interfaces to accept HVs. The system
855 needs to be per-operating-system and per-file-system
856 hookable/filterable, preferably both from XS and Perl level
857 (L<perlport/"Files and Filesystems"> is good reading at this point,
858 in fact, all of L<perlport> is.)
860 This has actually already been implemented (but only for Win32),
861 take a look at F<iperlsys.h> and F<win32/perlhost.h>. While all Win32
862 variants go through a set of "vtables" for operating system access,
863 non-Win32 systems currently go straight for the POSIX/UNIX-style
864 system/library call. Similar system as for Win32 should be
865 implemented for all platforms. The existing Win32 implementation
866 probably does not need to survive alongside this proposed new
867 implementation, the approaches could be merged.
869 What would this give us? One often-asked-for feature this would
870 enable is using Unicode for filenames, and other "names" like %ENV,
871 usernames, hostnames, and so forth.
872 (See L<perlunicode/"When Unicode Does Not Happen">.)
874 But this kind of virtualization would also allow for things like
875 virtual filesystems, virtual networks, and "sandboxes" (though as long
876 as dynamic loading of random object code is allowed, not very safe
877 sandboxes since external code of course know not of Perl's vtables).
878 An example of a smaller "sandbox" is that this feature can be used to
879 implement per-thread working directories: Win32 already does this.
881 See also L</"Extend PerlIO and PerlIO::Scalar">.
883 =head2 Investigate PADTMP hash pessimisation
885 The peephole optimier converts constants used for hash key lookups to shared
886 hash key scalars. Under ithreads, something is undoing this work. See
887 See http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html
891 Tasks that will get your name mentioned in the description of the "Highlights
894 =head2 make ithreads more robust
896 Generally make ithreads more robust. See also L</iCOW>
898 This task is incremental - even a little bit of work on it will help, and
899 will be greatly appreciated.
901 One bit would be to write the missing code in sv.c:Perl_dirp_dup.
903 Fix Perl_sv_dup, et al so that threads can return objects.
907 Sarathy and Arthur have a proposal for an improved Copy On Write which
908 specifically will be able to COW new ithreads. If this can be implemented
909 it would be a good thing.
911 =head2 (?{...}) closures in regexps
913 Fix (or rewrite) the implementation of the C</(?{...})/> closures.
915 =head2 A re-entrant regexp engine
917 This will allow the use of a regex from inside (?{ }), (??{ }) and
918 (?(?{ })|) constructs.
920 =head2 Add class set operations to regexp engine
922 Apparently these are quite useful. Anyway, Jeffery Friedl wants them.
924 demerphq has this on his todo list, but right at the bottom.