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Diffstat (limited to 'lib/SelfLoader.pm')
| -rw-r--r-- | lib/SelfLoader.pm | 131 |
1 files changed, 69 insertions, 62 deletions
diff --git a/lib/SelfLoader.pm b/lib/SelfLoader.pm index e3da9ebadb..136d42bef1 100644 --- a/lib/SelfLoader.pm +++ b/lib/SelfLoader.pm @@ -119,117 +119,123 @@ SelfLoader - load functions only on demand =head1 DESCRIPTION This module tells its users that functions in the FOOBAR package are to be -autoloaded from after the __DATA__ token. See also L<perlsub/"Autoloading">. +autoloaded from after the C<__DATA__> token. See also +L<perlsub/"Autoloading">. =head2 The __DATA__ token -The __DATA__ token tells the perl compiler that the perl code -for compilation is finished. Everything after the __DATA__ token +The C<__DATA__> token tells the perl compiler that the perl code +for compilation is finished. Everything after the C<__DATA__> token is available for reading via the filehandle FOOBAR::DATA, -where FOOBAR is the name of the current package when the __DATA__ -token is reached. This works just the same as __END__ does in -package 'main', but for other modules data after __END__ is not -automatically retreivable , whereas data after __DATA__ is. -The __DATA__ token is not recognized in versions of perl prior to +where FOOBAR is the name of the current package when the C<__DATA__> +token is reached. This works just the same as C<__END__> does in +package 'main', but for other modules data after C<__END__> is not +automatically retreivable , whereas data after C<__DATA__> is. +The C<__DATA__> token is not recognized in versions of perl prior to 5.001m. -Note that it is possible to have __DATA__ tokens in the same package -in multiple files, and that the last __DATA__ token in a given +Note that it is possible to have C<__DATA__> tokens in the same package +in multiple files, and that the last C<__DATA__> token in a given package that is encountered by the compiler is the one accessible -by the filehandle. This also applies to __END__ and main, i.e. if -the 'main' program has an __END__, but a module 'require'd (_not_ 'use'd) -by that program has a 'package main;' declaration followed by an '__DATA__', -then the DATA filehandle is set to access the data after the __DATA__ -in the module, _not_ the data after the __END__ token in the 'main' +by the filehandle. This also applies to C<__END__> and main, i.e. if +the 'main' program has an C<__END__>, but a module 'require'd (_not_ 'use'd) +by that program has a 'package main;' declaration followed by an 'C<__DATA__>', +then the C<DATA> filehandle is set to access the data after the C<__DATA__> +in the module, _not_ the data after the C<__END__> token in the 'main' program, since the compiler encounters the 'require'd file later. =head2 SelfLoader autoloading -The SelfLoader works by the user placing the __DATA__ -token _after_ perl code which needs to be compiled and -run at 'require' time, but _before_ subroutine declarations +The B<SelfLoader> works by the user placing the C<__DATA__> +token I<after> perl code which needs to be compiled and +run at 'require' time, but I<before> subroutine declarations that can be loaded in later - usually because they may never be called. -The SelfLoader will read from the FOOBAR::DATA filehandle to -load in the data after __DATA__, and load in any subroutine +The B<SelfLoader> will read from the FOOBAR::DATA filehandle to +load in the data after C<__DATA__>, and load in any subroutine when it is called. The costs are the one-time parsing of the -data after __DATA__, and a load delay for the _first_ +data after C<__DATA__>, and a load delay for the _first_ call of any autoloaded function. The benefits (hopefully) are a speeded up compilation phase, with no need to load functions which are never used. -The SelfLoader will stop reading from __DATA__ if -it encounters the __END__ token - just as you would expect. -If the __END__ token is present, and is followed by the -token DATA, then the SelfLoader leaves the FOOBAR::DATA +The B<SelfLoader> will stop reading from C<__DATA__> if +it encounters the C<__END__> token - just as you would expect. +If the C<__END__> token is present, and is followed by the +token DATA, then the B<SelfLoader> leaves the FOOBAR::DATA filehandle open on the line after that token. -The SelfLoader exports the AUTOLOAD subroutine to the -package using the SelfLoader, and this loads the called +The B<SelfLoader> exports the C<AUTOLOAD> subroutine to the +package using the B<SelfLoader>, and this loads the called subroutine when it is first called. There is no advantage to putting subroutines which will _always_ -be called after the __DATA__ token. +be called after the C<__DATA__> token. =head2 Autoloading and package lexicals A 'my $pack_lexical' statement makes the variable $pack_lexical -local _only_ to the file up to the __DATA__ token. Subroutines +local _only_ to the file up to the C<__DATA__> token. Subroutines declared elsewhere _cannot_ see these types of variables, just as if you declared subroutines in the package but in another file, they cannot see these variables. So specifically, autoloaded functions cannot see package -lexicals (this applies to both the SelfLoader and the Autoloader). +lexicals (this applies to both the B<SelfLoader> and the Autoloader). +The C<vars> pragma provides an alternative to defining package-level +globals that will be visible to autoloaded routines. See the documentation +on B<vars> in the pragma section of L<perlmod>. =head2 SelfLoader and AutoLoader -The SelfLoader can replace the AutoLoader - just change 'use AutoLoader' -to 'use SelfLoader' (though note that the SelfLoader exports +The B<SelfLoader> can replace the AutoLoader - just change 'use AutoLoader' +to 'use SelfLoader' (though note that the B<SelfLoader> exports the AUTOLOAD function - but if you have your own AUTOLOAD and are using the AutoLoader too, you probably know what you're doing), -and the __END__ token to __DATA__. You will need perl version 5.001m +and the C<__END__> token to C<__DATA__>. You will need perl version 5.001m or later to use this (version 5.001 with all patches up to patch m). -There is no need to inherit from the SelfLoader. +There is no need to inherit from the B<SelfLoader>. -The SelfLoader works similarly to the AutoLoader, but picks up the -subs from after the __DATA__ instead of in the 'lib/auto' directory. +The B<SelfLoader> works similarly to the AutoLoader, but picks up the +subs from after the C<__DATA__> instead of in the 'lib/auto' directory. There is a maintainance gain in not needing to run AutoSplit on the module at installation, and a runtime gain in not needing to keep opening and closing files to load subs. There is a runtime loss in needing -to parse the code after the __DATA__. +to parse the code after the C<__DATA__>. Details of the B<AutoLoader> and +another view of these distinctions can be found in that module's +documentation. =head2 __DATA__, __END__, and the FOOBAR::DATA filehandle. This section is only relevant if you want to use -the FOOBAR::DATA together with the SelfLoader. - -Data after the __DATA__ token in a module is read using the -FOOBAR::DATA filehandle. __END__ can still be used to denote the end -of the __DATA__ section if followed by the token DATA - this is supported -by the SelfLoader. The FOOBAR::DATA filehandle is left open if an __END__ -followed by a DATA is found, with the filehandle positioned at the start -of the line after the __END__ token. If no __END__ token is present, -or an __END__ token with no DATA token on the same line, then the filehandle -is closed. - -The SelfLoader reads from wherever the current -position of the FOOBAR::DATA filehandle is, until the -EOF or __END__. This means that if you want to use +the C<FOOBAR::DATA> together with the B<SelfLoader>. + +Data after the C<__DATA__> token in a module is read using the +FOOBAR::DATA filehandle. C<__END__> can still be used to denote the end +of the C<__DATA__> section if followed by the token DATA - this is supported +by the B<SelfLoader>. The C<FOOBAR::DATA> filehandle is left open if an +C<__END__> followed by a DATA is found, with the filehandle positioned at +the start of the line after the C<__END__> token. If no C<__END__> token is +present, or an C<__END__> token with no DATA token on the same line, then +the filehandle is closed. + +The B<SelfLoader> reads from wherever the current +position of the C<FOOBAR::DATA> filehandle is, until the +EOF or C<__END__>. This means that if you want to use that filehandle (and ONLY if you want to), you should either 1. Put all your subroutine declarations immediately after -the __DATA__ token and put your own data after those -declarations, using the __END__ token to mark the end -of subroutine declarations. You must also ensure that the SelfLoader +the C<__DATA__> token and put your own data after those +declarations, using the C<__END__> token to mark the end +of subroutine declarations. You must also ensure that the B<SelfLoader> reads first by calling 'SelfLoader->load_stubs();', or by using a function which is selfloaded; or -2. You should read the FOOBAR::DATA filehandle first, leaving +2. You should read the C<FOOBAR::DATA> filehandle first, leaving the handle open and positioned at the first line of subroutine declarations. @@ -255,8 +261,8 @@ properly. You can load the stubs into the module at 'require' time, by adding the statement 'SelfLoader->load_stubs();' to the module to do this. -The alternative is to put the stubs in before the __DATA__ token BEFORE -releasing the module, and for this purpose the Devel::SelfStubber +The alternative is to put the stubs in before the C<__DATA__> token BEFORE +releasing the module, and for this purpose the C<Devel::SelfStubber> module is available. However this does require the extra step of ensuring that the stubs are in the module. If this is done I strongly recommend that this is done BEFORE releasing the module - it should NOT be done @@ -265,10 +271,10 @@ at install time in general. =head1 Multiple packages and fully qualified subroutine names Subroutines in multiple packages within the same file are supported - but you -should note that this requires exporting the SelfLoader::AUTOLOAD to +should note that this requires exporting the C<SelfLoader::AUTOLOAD> to every package which requires it. This is done automatically by the -SelfLoader when it first loads the subs into the cache, but you should -really specify it in the initialization before the __DATA__ by putting +B<SelfLoader> when it first loads the subs into the cache, but you should +really specify it in the initialization before the C<__DATA__> by putting a 'use SelfLoader' statement in each package. Fully qualified subroutine names are also supported. For example, @@ -278,8 +284,9 @@ Fully qualified subroutine names are also supported. For example, package baz; sub dob {32} -will all be loaded correctly by the SelfLoader, and the SelfLoader +will all be loaded correctly by the B<SelfLoader>, and the B<SelfLoader> will ensure that the packages 'foo' and 'baz' correctly have the -SelfLoader AUTOLOAD method when the data after __DATA__ is first parsed. +B<SelfLoader> C<AUTOLOAD> method when the data after C<__DATA__> is first +parsed. =cut |