lib/perl5/5.8.8/AutoLoader.pm

   1 package AutoLoader;
   2
   3 use strict;
   4 use 5.006_001;
   5
   6 our($VERSION, $AUTOLOAD);
   7
   8 my $is_dosish;
   9 my $is_epoc;
  10 my $is_vms;
  11 my $is_macos;
  12
  13 BEGIN {
  14     $is_dosish = $^O eq 'dos' || $^O eq 'os2' || $^O eq 'MSWin32' || $^O eq 'NetWare';
  15     $is_epoc = $^O eq 'epoc';
  16     $is_vms = $^O eq 'VMS';
  17     $is_macos = $^O eq 'MacOS';
  18     $VERSION = '5.60';
  19 }
  20
  21 AUTOLOAD {
  22     my $sub = $AUTOLOAD;
  23     my $filename;
  24     # Braces used to preserve $1 et al.
  25     {
  26         # Try to find the autoloaded file from the package-qualified
  27         # name of the sub. e.g., if the sub needed is
  28         # Getopt::Long::GetOptions(), then $INC{Getopt/Long.pm} is
  29         # something like '/usr/lib/perl5/Getopt/Long.pm', and the
  30         # autoload file is '/usr/lib/perl5/auto/Getopt/Long/GetOptions.al'.
  31         #
  32         # However, if @INC is a relative path, this might not work.  If,
  33         # for example, @INC = ('lib'), then $INC{Getopt/Long.pm} is
  34         # 'lib/Getopt/Long.pm', and we want to require
  35         # 'auto/Getopt/Long/GetOptions.al' (without the leading 'lib').
  36         # In this case, we simple prepend the 'auto/' and let the
  37         # C<require> take care of the searching for us.
  38
  39         my ($pkg,$func) = ($sub =~ /(.*)::([^:]+)$/);
  40         $pkg =~ s#::#/#g;
  41         if (defined($filename = $INC{"$pkg.pm"})) {
  42             if ($is_macos) {
  43                 $pkg =~ tr#/#:#;
  44                 $filename =~ s#^(.*)$pkg\.pm\z#$1auto:$pkg:$func.al#s;
  45             } else {
  46                 $filename =~ s#^(.*)$pkg\.pm\z#$1auto/$pkg/$func.al#s;
  47             }
  48
  49             # if the file exists, then make sure that it is a
  50             # a fully anchored path (i.e either '/usr/lib/auto/foo/bar.al',
  51             # or './lib/auto/foo/bar.al'.  This avoids C<require> searching
  52             # (and failing) to find the 'lib/auto/foo/bar.al' because it
  53             # looked for 'lib/lib/auto/foo/bar.al', given @INC = ('lib').
  54
  55             if (-r $filename) {
  56                 unless ($filename =~ m|^/|s) {
  57                     if ($is_dosish) {
  58                         unless ($filename =~ m{^([a-z]:)?[\\/]}is) {
  59                              if ($^O ne 'NetWare') {
  60                                         $filename = "./$filename";
  61                                 } else {
  62                                         $filename = "$filename";
  63                                 }
  64                         }
  65                     }
  66                     elsif ($is_epoc) {
  67                         unless ($filename =~ m{^([a-z?]:)?[\\/]}is) {
  68                              $filename = "./$filename";
  69                         }
  70                     }
  71                     elsif ($is_vms) {
  72                         # XXX todo by VMSmiths
  73                         $filename = "./$filename";
  74                     }
  75                     elsif (!$is_macos) {
  76                         $filename = "./$filename";
  77                     }
  78                 }
  79             }
  80             else {
  81                 $filename = undef;
  82             }
  83         }
  84         unless (defined $filename) {
  85             # let C<require> do the searching
  86             $filename = "auto/$sub.al";
  87             $filename =~ s#::#/#g;
  88         }
  89     }
  90     my $save = $@;
  91     local $!; # Do not munge the value.
  92     eval { local $SIG{__DIE__}; require $filename };
  93     if ($@) {
  94         if (substr($sub,-9) eq '::DESTROY') {
  95             no strict 'refs';
  96             *$sub = sub {};
  97             $@ = undef;
  98         } elsif ($@ =~ /^Can't locate/) {
  99             # The load might just have failed because the filename was too
 100             # long for some old SVR3 systems which treat long names as errors.
 101             # If we can successfully truncate a long name then it's worth a go.
 102             # There is a slight risk that we could pick up the wrong file here
 103             # but autosplit should have warned about that when splitting.
 104             if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){
 105                 eval { local $SIG{__DIE__}; require $filename };
 106             }
 107         }
 108         if ($@){
 109             $@ =~ s/ at .*\n//;
 110             my $error = $@;
 111             require Carp;
 112             Carp::croak($error);
 113         }
 114     }
 115     $@ = $save;
 116     goto &$sub;
 117 }
 118
 119 sub import {
 120     my $pkg = shift;
 121     my $callpkg = caller;
 122
 123     #
 124     # Export symbols, but not by accident of inheritance.
 125     #
 126
 127     if ($pkg eq 'AutoLoader') {
 128         no strict 'refs';
 129         *{ $callpkg . '::AUTOLOAD' } = \&AUTOLOAD
 130             if @_ and $_[0] =~ /^&?AUTOLOAD$/;
 131     }
 132
 133     #
 134     # Try to find the autosplit index file.  Eg., if the call package
 135     # is POSIX, then $INC{POSIX.pm} is something like
 136     # '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in
 137     # '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that.
 138     #
 139     # However, if @INC is a relative path, this might not work.  If,
 140     # for example, @INC = ('lib'), then
 141     # $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require
 142     # 'auto/POSIX/autosplit.ix' (without the leading 'lib').
 143     #
 144
 145     (my $calldir = $callpkg) =~ s#::#/#g;
 146     my $path = $INC{$calldir . '.pm'};
 147     if (defined($path)) {
 148         # Try absolute path name.
 149         if ($is_macos) {
 150             (my $malldir = $calldir) =~ tr#/#:#;
 151             $path =~ s#^(.*)$malldir\.pm\z#$1auto:$malldir:autosplit.ix#s;
 152         } else {
 153             $path =~ s#^(.*)$calldir\.pm\z#$1auto/$calldir/autosplit.ix#;
 154         }
 155
 156         eval { require $path; };
 157         # If that failed, try relative path with normal @INC searching.
 158         if ($@) {
 159             $path ="auto/$calldir/autosplit.ix";
 160             eval { require $path; };
 161         }
 162         if ($@) {
 163             my $error = $@;
 164             require Carp;
 165             Carp::carp($error);
 166         }
 167     }
 168 }
 169
 170 sub unimport {
 171     my $callpkg = caller;
 172
 173     no strict 'refs';
 174     my $symname = $callpkg . '::AUTOLOAD';
 175     undef *{ $symname } if \&{ $symname } == \&AUTOLOAD;
 176     *{ $symname } = \&{ $symname };
 177 }
 178
 179 1;
 180
 181 __END__
 182
 183 =head1 NAME
 184
 185 AutoLoader - load subroutines only on demand
 186
 187 =head1 SYNOPSIS
 188
 189     package Foo;
 190     use AutoLoader 'AUTOLOAD';   # import the default AUTOLOAD subroutine
 191
 192     package Bar;
 193     use AutoLoader;              # don't import AUTOLOAD, define our own
 194     sub AUTOLOAD {
 195         ...
 196         $AutoLoader::AUTOLOAD = "...";
 197         goto &AutoLoader::AUTOLOAD;
 198     }
 199
 200 =head1 DESCRIPTION
 201
 202 The B<AutoLoader> module works with the B<AutoSplit> module and the
 203 C<__END__> token to defer the loading of some subroutines until they are
 204 used rather than loading them all at once.
 205
 206 To use B<AutoLoader>, the author of a module has to place the
 207 definitions of subroutines to be autoloaded after an C<__END__> token.
 208 (See L<perldata>.)  The B<AutoSplit> module can then be run manually to
 209 extract the definitions into individual files F<auto/funcname.al>.
 210
 211 B<AutoLoader> implements an AUTOLOAD subroutine.  When an undefined
 212 subroutine in is called in a client module of B<AutoLoader>,
 213 B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a
 214 file with a name related to the location of the file from which the
 215 client module was read.  As an example, if F<POSIX.pm> is located in
 216 F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl
 217 subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where
 218 the C<.al> file has the same name as the subroutine, sans package.  If
 219 such a file exists, AUTOLOAD will read and evaluate it,
 220 thus (presumably) defining the needed subroutine.  AUTOLOAD will then
 221 C<goto> the newly defined subroutine.
 222
 223 Once this process completes for a given function, it is defined, so
 224 future calls to the subroutine will bypass the AUTOLOAD mechanism.
 225
 226 =head2 Subroutine Stubs
 227
 228 In order for object method lookup and/or prototype checking to operate
 229 correctly even when methods have not yet been defined it is necessary to
 230 "forward declare" each subroutine (as in C<sub NAME;>).  See
 231 L<perlsub/"SYNOPSIS">.  Such forward declaration creates "subroutine
 232 stubs", which are place holders with no code.
 233
 234 The AutoSplit and B<AutoLoader> modules automate the creation of forward
 235 declarations.  The AutoSplit module creates an 'index' file containing
 236 forward declarations of all the AutoSplit subroutines.  When the
 237 AutoLoader module is 'use'd it loads these declarations into its callers
 238 package.
 239
 240 Because of this mechanism it is important that B<AutoLoader> is always
 241 C<use>d and not C<require>d.
 242
 243 =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine
 244
 245 In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must>
 246 explicitly import it:
 247
 248     use AutoLoader 'AUTOLOAD';
 249
 250 =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine
 251
 252 Some modules, mainly extensions, provide their own AUTOLOAD subroutines.
 253 They typically need to check for some special cases (such as constants)
 254 and then fallback to B<AutoLoader>'s AUTOLOAD for the rest.
 255
 256 Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine.
 257 Instead, they should define their own AUTOLOAD subroutines along these
 258 lines:
 259
 260     use AutoLoader;
 261     use Carp;
 262
 263     sub AUTOLOAD {
 264         my $sub = $AUTOLOAD;
 265         (my $constname = $sub) =~ s/.*:://;
 266         my $val = constant($constname, @_ ? $_[0] : 0);
 267         if ($! != 0) {
 268             if ($! =~ /Invalid/ || $!{EINVAL}) {
 269                 $AutoLoader::AUTOLOAD = $sub;
 270                 goto &AutoLoader::AUTOLOAD;
 271             }
 272             else {
 273                 croak "Your vendor has not defined constant $constname";
 274             }
 275         }
 276         *$sub = sub { $val }; # same as: eval "sub $sub { $val }";
 277         goto &$sub;
 278     }
 279
 280 If any module's own AUTOLOAD subroutine has no need to fallback to the
 281 AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit
 282 subroutines), then that module should not use B<AutoLoader> at all.
 283
 284 =head2 Package Lexicals
 285
 286 Package lexicals declared with C<my> in the main block of a package
 287 using B<AutoLoader> will not be visible to auto-loaded subroutines, due to
 288 the fact that the given scope ends at the C<__END__> marker.  A module
 289 using such variables as package globals will not work properly under the
 290 B<AutoLoader>.
 291
 292 The C<vars> pragma (see L<perlmod/"vars">) may be used in such
 293 situations as an alternative to explicitly qualifying all globals with
 294 the package namespace.  Variables pre-declared with this pragma will be
 295 visible to any autoloaded routines (but will not be invisible outside
 296 the package, unfortunately).
 297
 298 =head2 Not Using AutoLoader
 299
 300 You can stop using AutoLoader by simply
 301
 302         no AutoLoader;
 303
 304 =head2 B<AutoLoader> vs. B<SelfLoader>
 305
 306 The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the
 307 loading of subroutines.
 308
 309 B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>.
 310 While this avoids the use of a hierarchy of disk files and the
 311 associated open/close for each routine loaded, B<SelfLoader> suffers a
 312 startup speed disadvantage in the one-time parsing of the lines after
 313 C<__DATA__>, after which routines are cached.  B<SelfLoader> can also
 314 handle multiple packages in a file.
 315
 316 B<AutoLoader> only reads code as it is requested, and in many cases
 317 should be faster, but requires a mechanism like B<AutoSplit> be used to
 318 create the individual files.  L<ExtUtils::MakeMaker> will invoke
 319 B<AutoSplit> automatically if B<AutoLoader> is used in a module source
 320 file.
 321
 322 =head1 CAVEATS
 323
 324 AutoLoaders prior to Perl 5.002 had a slightly different interface.  Any
 325 old modules which use B<AutoLoader> should be changed to the new calling
 326 style.  Typically this just means changing a require to a use, adding
 327 the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader>
 328 from C<@ISA>.
 329
 330 On systems with restrictions on file name length, the file corresponding
 331 to a subroutine may have a shorter name that the routine itself.  This
 332 can lead to conflicting file names.  The I<AutoSplit> package warns of
 333 these potential conflicts when used to split a module.
 334
 335 AutoLoader may fail to find the autosplit files (or even find the wrong
 336 ones) in cases where C<@INC> contains relative paths, B<and> the program
 337 does C<chdir>.
 338
 339 =head1 SEE ALSO
 340
 341 L<SelfLoader> - an autoloader that doesn't use external files.
 342
 343 =cut