From: Ilya Zakharevich Date: Fri, 21 Mar 1997 00:34:30 +0000 (-0500) Subject: New module: autouse.pm X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=6757905eccb6dd0440ef65e8128a277a20f7d943;p=p5sagit%2Fp5-mst-13.2.git New module: autouse.pm Subject: Newer autouse.pm I included support for prototypes (and some warnings in POD) into the package, but cannot fully check them, since they trigger a lot of bugs in support of prototypes in Perl. I hope that when the bugs are corrected, this will work better. Enjoy, p5p-msgid: 199703210034.TAA13469@monk.mps.ohio-state.edu --- diff --git a/lib/autouse.pm b/lib/autouse.pm new file mode 100644 index 0000000..13bc597 --- /dev/null +++ b/lib/autouse.pm @@ -0,0 +1,176 @@ +package autouse; +#use strict; # debugging only +use 5.003_90; # ->can + +$autouse::VERSION = '0.02'; + +my $debug = 0; + +my %disable_w; + +sub croak { + require Carp; + Carp::croak(@_); +} + +sub import { + shift; + my $module = shift; + if (exists $INC{"$module.pm"}) { + unless (exists $INC{"Exporter.pm"}) { + croak("use autouse with a module which has its own import()") + if $module->can('import'); + return; # Ignore import + } + croak("use autouse with a module which has its own import()") + unless $module->can('import') == \&Exporter::import; + local $Exporter::ExportLevel = $Exporter::ExportLevel; + $Exporter::ExportLevel++; + # $Exporter::Verbose = 1; + my @args = @_; + my $f; + foreach $f (@args) { + next unless $f =~ s/\((.*)\)$//; + my $proto = $1; + my $sub = index($f, "::") != -1 ? $f : "$module" . "::$f"; + croak("Prototype mismatch on `$sub' when autousing `$module':\n", + "\t`$proto' specified, the real one `", + prototype($sub), "'") + unless prototype($sub) eq $proto; + } + return $module->import(@args); + } + # It is not loaded: need to do real work. + my $callpkg = caller(0); + print "called from `$callpkg'.\n" if $debug; + + my ($func, $index); + foreach $func (@_) { + my $proto; + $proto = $1 if $func =~ s/\((.*)\)$//; + my $closure_import_func = $func; # Full name + my $closure_func = $func; # Name inside package + $index = index($func, '::'); + + if ($index == -1) { + $closure_import_func = $callpkg . "::$func"; + } else { + $closure_func = substr $func, $index + 2; + croak("Trying to autouse into a different package") + unless substr($func, 0, $index) eq $module; + $disable_w{$module} = 1; + } + my $load_sub = sub { + { + local $^W = exists $disable_w{$module}; # Redefinition + eval "require $module"; + die $@ if $@; + croak("Prototype mismatch on `$closure_import_func' ", + "after loading `$module':\n", + "\t`$proto' specified when autousing, the real one `", + prototype($closure_import_func), "'") + if defined $proto + and prototype($closure_import_func) ne $proto; + local $^W = 0; # Redefinition + *$closure_import_func = \&{$module . "::$closure_func"} + unless \&$closure_import_func == \&{$module . "::$closure_func"}; + } + print "In loader for `$module: $closure_import_func => $closure_func'.\n" + if $debug; + goto &$closure_import_func; + }; + if (defined $proto) { + *$closure_import_func = eval "sub ($proto) {&\$load_sub}"; + } else { + *$closure_import_func = $load_sub; + } + } +} + +1; + +__END__ + +=head1 NAME + +autouse - postpone load of modules until a function is used + +=head1 SYNOPSIS + + use autouse 'Carp' => qw(carp croak); + carp "this carp was predeclared and autoused "; + + +=head1 DESCRIPTION + +If the module C is already loaded, then the declaration + + use autouse 'Module' => qw(func1 func2($;$) Module::func3); + +is equivalent to + + use Module qw(func1 func2); + +if C defines func2() with prototype C<($;$)>, and func1() and +func3() have no prototypes. (At least if C uses C's +C, otherwise it is a fatal error.) + +If the module C is not loaded yet, then the above declaration +declares functions func1() and func2() in the current package, and +declares a function Module::func3(). When these functions are called, +they load the package C if needed, and substitute themselves +with the correct definitions. + +=head1 WARNING + +Using C will move important steps of your program's execution +from compile time to runtime. This can + +=over + +=item * + +Break the execution of your program if the module you Cd has +some initialization which it expects to be done early. + +=item * + +hide bugs in your code since important checks (like correctness of +prototypes) is moved from compile time to runtime. In particular, if +the prototype you specified on C line is wrong, you will not +find it out until the corresponding function is executed. This will be +very unfortunate for functions which are not always called (note that +for such functions Cing gives biggest win, for a workaround +see below). + +=back + +To alleviate the second problem (partially) it is advised to write +your scripts like this: + + use Module; + use autouse Module => qw(carp($) croak(&$)); + carp "this carp was predeclared and autoused "; + +The first line ensures that the errors in your argument specification +are found early. When you ship your application you should comment +out the first line, since it makes the second one useless. + +=head1 BUGS + +If Module::func3() is autoused, and the module is loaded between the +C directive and a call to Module::func3(), warnings about +redefinition would appear if warnings are enabled. + +If Module::func3() is autoused, warnings are disabled when loading the +module via autoused functions. + +=head1 AUTHOR + +Ilya Zakharevich (ilya@math.ohio-state.edu) + +=head1 SEE ALSO + +perl(1). + +=cut