chocolateboy > Method-Lexical > Method::Lexical



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Method::Lexical - private methods and lexical method overrides


    package MyPragma;

    use base qw(Method::Lexical);

    sub import {
            'private'         => sub { ... },
            'UNIVERSAL::dump' => '+Data::Dump::pp'
    #!/usr/bin/env perl

    my $self = bless {};

        use MyPragma;

        $self->private(); # OK
        $self->dump();    # OK

    $self->private; # Can't locate object method "private" via package "main"
    $self->dump;    # Can't locate object method "dump" via package "main"


Method::Lexical is a lexically-scoped pragma that implements lexical methods i.e. methods whose use is restricted to the lexical scope in which they are imported or declared.

The use Method::Lexical statement takes a hashref or a list of key/value pairs in which the keys are method names and the values are subroutine references or strings containing the package-qualified name of the method to be called. Unqualifed method names in keys are installed as methods in the currently-compiling package. The following example summarizes the types of keys and values that can be supplied.

    use Method::Lexical {
        foo              => \&foo,               # unqualified method-name key: installed in the currently-compiling package e.g. main::foo
        MyClass::foo     => \&foo,               # qualified method-name key: installed in the specified package
        bar              => sub { ... },         # anonymous sub value
        baz              => \&baz,               # coderef value
        quux             => 'main::quux',        # sub name value: unqualified names are resolved to the currently-compiling package
        dump             => '+Data::Dump::dump', # autoload Data::Dump
       'UNIVERSAL::dump' => \&Data::Dump::dump,  # define a universal method
       'UNIVERSAL::isa'  => \&my_isa,            # override a universal method
      '-autoload'        => 1,                   # autoload modules for all subs passed by name
      '-debug'           => 1                    # show diagnostic messages


Method::Lexical options are prefixed with a hyphen to distinguish them from method names. The following options are supported.


If the value is a string containing a package-qualified subroutine name, then the subroutine's module is automatically loaded. This can either be done on a per-method basis by prefixing the value with a +, or for all value arguments with qualified names by supplying the -autoload option with a true value e.g.

    use Method::Lexical {
         foo       => 'MyFoo::foo',
         bar       => 'MyBar::bar',
         baz       => 'MyBaz::baz',
       '-autoload' => 1


    use MyFoo;
    use MyBaz;

    use Method::Lexical
         foo =>  'MyFoo::foo',
         bar => '+MyBar::bar', # autoload MyBar
         baz =>  'MyBaz::baz';

This option should not be confused with lexical AUTOLOAD methods, which are also supported e.g.

    use Method::Lexical
        AUTOLOAD             => sub { ... },
       'UNIVERSAL::AUTOLOAD' => \&autoload;


A trace of the module's actions can be enabled or disabled lexically by supplying the -debug option with a true or false value. The trace is printed to STDERR.


    use Method::Lexical {
         foo    => \&foo,
         bar    => sub { ... },
       '-debug' => 1



Method::Lexical::import can be called indirectly via use Method::Lexical or can be overridden by subclasses to create lexically-scoped pragmas that export methods whose use is restricted to the calling scope e.g.

    package Universal::Dump;

    use base qw(Method::Lexical);

    sub import { shift->SUPER::import('UNIVERSAL::dump' => '+Data::Dump::dump') }


Client code can then import lexical methods from the module:

    #!/usr/bin/env perl

    use CGI;

        use Universal::Dump;

        say CGI->new->dump; # OK

    eval { CGI->new->dump };
    warn $@; # Can't locate object method "dump" via package "CGI"


Method::Lexical::unimport removes the specified lexical methods from the current scope, or all lexical methods if no arguments are supplied.

    use Method::Lexical foo => \&foo;

    my $self = bless {};

        use Method::Lexical
             bar             => sub { ... },
            'UNIVERSAL::baz' => sub { ... };

        $self->foo(); # OK
        $self->bar(); # OK
        $self->baz(); # OK

        no Method::Lexical qw(foo);

        eval { $self->foo() };
        warn $@; # Can't locate object method "foo" via package "main"

        $self->bar(); # OK
        $self->baz(); # OK

        no Method::Lexical;

        eval { $self->bar() };
        warn $@; # Can't locate object method "bar" via package "main"

        eval { $self->baz() };
        warn $@; # Can't locate object method "baz" via package "main"

    $self->foo(); # OK

Unimports are specific to the class supplied in the no statement, so pragmas that subclass Method::Lexical inherit an unimport method that only removes the methods they installed e.g.

        use MyPragma qw(foo bar baz);

        use Method::Lexical quux => \&quux;

        $self->foo();  # OK
        $self->quux(); # OK

        no MyPragma qw(foo); # unimports foo
        no MyPragma;         # unimports bar and baz
        no Method::Lexical;  # unimports quux


Lexical methods must be defined before any invocations of those methods are compiled, otherwise those invocations will be compiled as ordinary method calls. This won't work:

    sub public {
        my $self = shift;
        $self->private(); # not a private method; compiled as an ordinary (public) method call

    use Method::Lexical private => sub { ... };

This works:

    use Method::Lexical private => sub { ... };

    sub public {
        my $self = shift;
        $self->private(); # OK

Method calls on glob or filehandle invocants are interpreted as ordinary method calls.

The method resolution order for lexical method calls on pre-5.10 perls is currently fixed at depth-first search.





chocolateboy <>


Copyright (C) 2009-2013 by chocolateboy

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.8 or, at your option, any later version of Perl 5 you may have available.

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