lib/perl5/5.6.1/SelfLoader.pm

   1 package SelfLoader;
   2 # use Carp;
   3 require Exporter;
   4 @ISA = qw(Exporter);
   5 @EXPORT = qw(AUTOLOAD);
   6 $VERSION = "1.0902";
   7 sub Version {$VERSION}
   8 $DEBUG = 0;
   9
  10 my %Cache;      # private cache for all SelfLoader's client packages
  11
  12 # allow checking for valid ': attrlist' attachments
  13 my $nested;
  14 $nested = qr{ \( (?: (?> [^()]+ ) | (??{ $nested }) )* \) }x;
  15 my $one_attr = qr{ (?> (?! \d) \w+ (?:$nested)? ) (?:\s*\:\s*|\s+(?!\:)) }x;
  16 my $attr_list = qr{ \s* : \s* (?: $one_attr )* }x;
  17
  18 sub croak { require Carp; goto &Carp::croak }
  19
  20 AUTOLOAD {
  21     print STDERR "SelfLoader::AUTOLOAD for $AUTOLOAD\n" if $DEBUG;
  22     my $SL_code = $Cache{$AUTOLOAD};
  23     my $save = $@; # evals in both AUTOLOAD and _load_stubs can corrupt $@
  24     unless ($SL_code) {
  25         # Maybe this pack had stubs before __DATA__, and never initialized.
  26         # Or, this maybe an automatic DESTROY method call when none exists.
  27         $AUTOLOAD =~ m/^(.*)::/;
  28         SelfLoader->_load_stubs($1) unless exists $Cache{"${1}::<DATA"};
  29         $SL_code = $Cache{$AUTOLOAD};
  30         $SL_code = "sub $AUTOLOAD { }"
  31             if (!$SL_code and $AUTOLOAD =~ m/::DESTROY$/);
  32         croak "Undefined subroutine $AUTOLOAD" unless $SL_code;
  33     }
  34     print STDERR "SelfLoader::AUTOLOAD eval: $SL_code\n" if $DEBUG;
  35
  36     eval $SL_code;
  37     if ($@) {
  38         $@ =~ s/ at .*\n//;
  39         croak $@;
  40     }
  41     $@ = $save;
  42     defined(&$AUTOLOAD) || die "SelfLoader inconsistency error";
  43     delete $Cache{$AUTOLOAD};
  44     goto &$AUTOLOAD
  45 }
  46
  47 sub load_stubs { shift->_load_stubs((caller)[0]) }
  48
  49 sub _load_stubs {
  50     my($self, $callpack) = @_;
  51     my $fh = \*{"${callpack}::DATA"};
  52     my $currpack = $callpack;
  53     my($line,$name,@lines, @stubs, $protoype);
  54
  55     print STDERR "SelfLoader::load_stubs($callpack)\n" if $DEBUG;
  56     croak("$callpack doesn't contain an __DATA__ token")
  57         unless fileno($fh);
  58     $Cache{"${currpack}::<DATA"} = 1;   # indicate package is cached
  59
  60     local($/) = "\n";
  61     while(defined($line = <$fh>) and $line !~ m/^__END__/) {
  62         if ($line =~ m/^sub\s+([\w:]+)\s*((?:\([\\\$\@\%\&\*\;]*\))?(?:$attr_list)?)/) {
  63             push(@stubs, $self->_add_to_cache($name, $currpack, \@lines, $protoype));
  64             $protoype = $2;
  65             @lines = ($line);
  66             if (index($1,'::') == -1) {         # simple sub name
  67                 $name = "${currpack}::$1";
  68             } else {                            # sub name with package
  69                 $name = $1;
  70                 $name =~ m/^(.*)::/;
  71                 if (defined(&{"${1}::AUTOLOAD"})) {
  72                     \&{"${1}::AUTOLOAD"} == \&SelfLoader::AUTOLOAD ||
  73                         die 'SelfLoader Error: attempt to specify Selfloading',
  74                             " sub $name in non-selfloading module $1";
  75                 } else {
  76                     $self->export($1,'AUTOLOAD');
  77                 }
  78             }
  79         } elsif ($line =~ m/^package\s+([\w:]+)/) { # A package declared
  80             push(@stubs, $self->_add_to_cache($name, $currpack, \@lines, $protoype));
  81             $self->_package_defined($line);
  82             $name = '';
  83             @lines = ();
  84             $currpack = $1;
  85             $Cache{"${currpack}::<DATA"} = 1;   # indicate package is cached
  86             if (defined(&{"${1}::AUTOLOAD"})) {
  87                 \&{"${1}::AUTOLOAD"} == \&SelfLoader::AUTOLOAD ||
  88                     die 'SelfLoader Error: attempt to specify Selfloading',
  89                         " package $currpack which already has AUTOLOAD";
  90             } else {
  91                 $self->export($currpack,'AUTOLOAD');
  92             }
  93         } else {
  94             push(@lines,$line);
  95         }
  96     }
  97     close($fh) unless defined($line) && $line =~ /^__END__\s*DATA/;     # __END__
  98     push(@stubs, $self->_add_to_cache($name, $currpack, \@lines, $protoype));
  99     eval join('', @stubs) if @stubs;
 100 }
 101
 102
 103 sub _add_to_cache {
 104     my($self,$fullname,$pack,$lines, $protoype) = @_;
 105     return () unless $fullname;
 106     (require Carp), Carp::carp("Redefining sub $fullname")
 107       if exists $Cache{$fullname};
 108     $Cache{$fullname} = join('', "package $pack; ",@$lines);
 109     print STDERR "SelfLoader cached $fullname: $Cache{$fullname}" if $DEBUG;
 110     # return stub to be eval'd
 111     defined($protoype) ? "sub $fullname $protoype;" : "sub $fullname;"
 112 }
 113
 114 sub _package_defined {}
 115
 116 1;
 117 __END__
 118
 119 =head1 NAME
 120
 121 SelfLoader - load functions only on demand
 122
 123 =head1 SYNOPSIS
 124
 125     package FOOBAR;
 126     use SelfLoader;
 127
 128     ... (initializing code)
 129
 130     __DATA__
 131     sub {....
 132
 133
 134 =head1 DESCRIPTION
 135
 136 This module tells its users that functions in the FOOBAR package are to be
 137 autoloaded from after the C<__DATA__> token.  See also
 138 L<perlsub/"Autoloading">.
 139
 140 =head2 The __DATA__ token
 141
 142 The C<__DATA__> token tells the perl compiler that the perl code
 143 for compilation is finished. Everything after the C<__DATA__> token
 144 is available for reading via the filehandle FOOBAR::DATA,
 145 where FOOBAR is the name of the current package when the C<__DATA__>
 146 token is reached. This works just the same as C<__END__> does in
 147 package 'main', but for other modules data after C<__END__> is not
 148 automatically retrievable, whereas data after C<__DATA__> is.
 149 The C<__DATA__> token is not recognized in versions of perl prior to
 150 5.001m.
 151
 152 Note that it is possible to have C<__DATA__> tokens in the same package
 153 in multiple files, and that the last C<__DATA__> token in a given
 154 package that is encountered by the compiler is the one accessible
 155 by the filehandle. This also applies to C<__END__> and main, i.e. if
 156 the 'main' program has an C<__END__>, but a module 'require'd (_not_ 'use'd)
 157 by that program has a 'package main;' declaration followed by an 'C<__DATA__>',
 158 then the C<DATA> filehandle is set to access the data after the C<__DATA__>
 159 in the module, _not_ the data after the C<__END__> token in the 'main'
 160 program, since the compiler encounters the 'require'd file later.
 161
 162 =head2 SelfLoader autoloading
 163
 164 The B<SelfLoader> works by the user placing the C<__DATA__>
 165 token I<after> perl code which needs to be compiled and
 166 run at 'require' time, but I<before> subroutine declarations
 167 that can be loaded in later - usually because they may never
 168 be called.
 169
 170 The B<SelfLoader> will read from the FOOBAR::DATA filehandle to
 171 load in the data after C<__DATA__>, and load in any subroutine
 172 when it is called. The costs are the one-time parsing of the
 173 data after C<__DATA__>, and a load delay for the _first_
 174 call of any autoloaded function. The benefits (hopefully)
 175 are a speeded up compilation phase, with no need to load
 176 functions which are never used.
 177
 178 The B<SelfLoader> will stop reading from C<__DATA__> if
 179 it encounters the C<__END__> token - just as you would expect.
 180 If the C<__END__> token is present, and is followed by the
 181 token DATA, then the B<SelfLoader> leaves the FOOBAR::DATA
 182 filehandle open on the line after that token.
 183
 184 The B<SelfLoader> exports the C<AUTOLOAD> subroutine to the
 185 package using the B<SelfLoader>, and this loads the called
 186 subroutine when it is first called.
 187
 188 There is no advantage to putting subroutines which will _always_
 189 be called after the C<__DATA__> token.
 190
 191 =head2 Autoloading and package lexicals
 192
 193 A 'my $pack_lexical' statement makes the variable $pack_lexical
 194 local _only_ to the file up to the C<__DATA__> token. Subroutines
 195 declared elsewhere _cannot_ see these types of variables,
 196 just as if you declared subroutines in the package but in another
 197 file, they cannot see these variables.
 198
 199 So specifically, autoloaded functions cannot see package
 200 lexicals (this applies to both the B<SelfLoader> and the Autoloader).
 201 The C<vars> pragma provides an alternative to defining package-level
 202 globals that will be visible to autoloaded routines. See the documentation
 203 on B<vars> in the pragma section of L<perlmod>.
 204
 205 =head2 SelfLoader and AutoLoader
 206
 207 The B<SelfLoader> can replace the AutoLoader - just change 'use AutoLoader'
 208 to 'use SelfLoader' (though note that the B<SelfLoader> exports
 209 the AUTOLOAD function - but if you have your own AUTOLOAD and
 210 are using the AutoLoader too, you probably know what you're doing),
 211 and the C<__END__> token to C<__DATA__>. You will need perl version 5.001m
 212 or later to use this (version 5.001 with all patches up to patch m).
 213
 214 There is no need to inherit from the B<SelfLoader>.
 215
 216 The B<SelfLoader> works similarly to the AutoLoader, but picks up the
 217 subs from after the C<__DATA__> instead of in the 'lib/auto' directory.
 218 There is a maintenance gain in not needing to run AutoSplit on the module
 219 at installation, and a runtime gain in not needing to keep opening and
 220 closing files to load subs. There is a runtime loss in needing
 221 to parse the code after the C<__DATA__>. Details of the B<AutoLoader> and
 222 another view of these distinctions can be found in that module's
 223 documentation.
 224
 225 =head2 __DATA__, __END__, and the FOOBAR::DATA filehandle.
 226
 227 This section is only relevant if you want to use
 228 the C<FOOBAR::DATA> together with the B<SelfLoader>.
 229
 230 Data after the C<__DATA__> token in a module is read using the
 231 FOOBAR::DATA filehandle. C<__END__> can still be used to denote the end
 232 of the C<__DATA__> section if followed by the token DATA - this is supported
 233 by the B<SelfLoader>. The C<FOOBAR::DATA> filehandle is left open if an
 234 C<__END__> followed by a DATA is found, with the filehandle positioned at
 235 the start of the line after the C<__END__> token. If no C<__END__> token is
 236 present, or an C<__END__> token with no DATA token on the same line, then
 237 the filehandle is closed.
 238
 239 The B<SelfLoader> reads from wherever the current
 240 position of the C<FOOBAR::DATA> filehandle is, until the
 241 EOF or C<__END__>. This means that if you want to use
 242 that filehandle (and ONLY if you want to), you should either
 243
 244 1. Put all your subroutine declarations immediately after
 245 the C<__DATA__> token and put your own data after those
 246 declarations, using the C<__END__> token to mark the end
 247 of subroutine declarations. You must also ensure that the B<SelfLoader>
 248 reads first by  calling 'SelfLoader-E<gt>load_stubs();', or by using a
 249 function which is selfloaded;
 250
 251 or
 252
 253 2. You should read the C<FOOBAR::DATA> filehandle first, leaving
 254 the handle open and positioned at the first line of subroutine
 255 declarations.
 256
 257 You could conceivably do both.
 258
 259 =head2 Classes and inherited methods.
 260
 261 For modules which are not classes, this section is not relevant.
 262 This section is only relevant if you have methods which could
 263 be inherited.
 264
 265 A subroutine stub (or forward declaration) looks like
 266
 267   sub stub;
 268
 269 i.e. it is a subroutine declaration without the body of the
 270 subroutine. For modules which are not classes, there is no real
 271 need for stubs as far as autoloading is concerned.
 272
 273 For modules which ARE classes, and need to handle inherited methods,
 274 stubs are needed to ensure that the method inheritance mechanism works
 275 properly. You can load the stubs into the module at 'require' time, by
 276 adding the statement 'SelfLoader-E<gt>load_stubs();' to the module to do
 277 this.
 278
 279 The alternative is to put the stubs in before the C<__DATA__> token BEFORE
 280 releasing the module, and for this purpose the C<Devel::SelfStubber>
 281 module is available.  However this does require the extra step of ensuring
 282 that the stubs are in the module. If this is done I strongly recommend
 283 that this is done BEFORE releasing the module - it should NOT be done
 284 at install time in general.
 285
 286 =head1 Multiple packages and fully qualified subroutine names
 287
 288 Subroutines in multiple packages within the same file are supported - but you
 289 should note that this requires exporting the C<SelfLoader::AUTOLOAD> to
 290 every package which requires it. This is done automatically by the
 291 B<SelfLoader> when it first loads the subs into the cache, but you should
 292 really specify it in the initialization before the C<__DATA__> by putting
 293 a 'use SelfLoader' statement in each package.
 294
 295 Fully qualified subroutine names are also supported. For example,
 296
 297    __DATA__
 298    sub foo::bar {23}
 299    package baz;
 300    sub dob {32}
 301
 302 will all be loaded correctly by the B<SelfLoader>, and the B<SelfLoader>
 303 will ensure that the packages 'foo' and 'baz' correctly have the
 304 B<SelfLoader> C<AUTOLOAD> method when the data after C<__DATA__> is first
 305 parsed.
 306
 307 =cut