NAME

       Lexical::Sub - subroutines without namespace pollution

SYNOPSIS

               use Lexical::Sub quux => sub { $_[0] + 1 };
               use Lexical::Sub carp => \&Carp::carp;

DESCRIPTION

       This module implements lexical scoping of subroutines.  Although it can be used directly,
       it is mainly intended to be infrastructure for modules that manage namespaces.

       This module influences the meaning of single-part subroutine names that appear directly in
       code, such as "&foo" and ""foo(123)"".  Normally, in the absence of any particular
       declaration, these would refer to the subroutine of that name located in the current
       package.  A "Lexical::Sub" declaration can change this to refer to any particular
       subroutine, bypassing the package system entirely.  A subroutine name that includes an
       explicit package part, such as "&main::foo", always refers to the subroutine in the
       specified package, and is unaffected by this module.  A symbolic reference through a
       string value, such as ""&{'foo'}"", also looks in the package system, and so is unaffected
       by this module.

       Bareword references to subroutines, such as ""foo(123)"", only work on Perl 5.11.2 and
       later.  On earlier Perls you must use the "&" sigil, as in ""&foo(123)"".

       A name definition supplied by this module takes effect from the end of the definition
       statement up to the end of the immediately enclosing block, except where it is shadowed
       within a nested block.  This is the same lexical scoping that the "my", "our", and "state"
       keywords supply.  These lexical definitions propagate into string "eval"s, on Perl
       versions that support it (5.9.3 and later).

       This module is implemented through the mechanism of Lexical::Var.  Its distinct name and
       declaration syntax exist to make lexical subroutine declarations clearer.

PACKAGE METHODS

       These methods are meant to be invoked on the "Lexical::Sub" package.

       Lexical::Sub->import(NAME => REF, ...)
           Sets up lexical subroutine declarations, in the lexical environment that is currently
           compiling.  Each NAME must be a bare subroutine name (e.g., "foo"), and each REF must
           be a reference to a subroutine.  The name is lexically associated with the referenced
           subroutine.

       Lexical::Sub->unimport(NAME [=> REF], ...)
           Sets up negative lexical subroutine declarations, in the lexical environment that is
           currently compiling.  Each NAME must be a bare subroutine name (e.g., "foo").  If the
           name is given on its own, it is lexically dissociated from any subroutine.  Within the
           resulting scope, the subroutine name will not be recognised.  If a REF (which must be
           a reference to a subroutine) is specified with a name, the name will be dissociated if
           and only if it is currently associated with that subroutine.

BUGS

       Subroutine invocations without the "&" sigil cannot be correctly processed on Perl
       versions earlier than 5.11.2.  This is because the parser needs to look up the subroutine
       early, in order to let any prototype affect parsing, and it looks up the subroutine by a
       different mechanism than is used to generate the call op.  (Some forms of sigilless call
       have other complications of a similar nature.)  If an attempt is made to call a lexical
       subroutine via a bareword on an older Perl, this module will probably still be able to
       intercept the call op, and will throw an exception to indicate that the parsing has gone
       wrong.  However, in some cases compilation goes further wrong before this module can catch
       it, resulting in either a confusing parse error or (in rare situations) silent compilation
       to an incorrect op sequence.  On Perl 5.11.2 and later, sigilless subroutine calls work
       correctly, except for an issue noted below.

       Subroutine calls that have neither sigil nor parentheses (around the argument list) are
       subject to an ambiguity with indirect object syntax.  If the first argument expression
       begins with a bareword or a scalar variable reference then the Perl parser is liable to
       interpret the call as an indirect method call.  Normally this syntax would be interpreted
       as a subroutine call if the subroutine exists, but the parser doesn't look at lexically-
       defined subroutines for this purpose.  The call interpretation can be forced by prefixing
       the first argument expression with a "+", or by wrapping the whole argument list in
       parentheses.

       Package hash entries get created for subroutine names that are used, even though the
       subroutines are not actually being stored or looked up in the package.  This can
       occasionally result in a "used only once" warning failing to occur when it should.

       On Perls prior to 5.15.5, if this package's "import" or "unimport" method is called from
       inside a string "eval" inside a "BEGIN" block, it does not have proper access to the
       compiling environment, and will complain that it is being invoked outside compilation.
       Calling from the body of a "require"d or "do"ed file causes the same problem on the same
       Perl versions.  Other kinds of indirection within a "BEGIN" block, such as calling via a
       normal function, do not cause this problem.

SEE ALSO

       Lexical::Import, Lexical::Var

AUTHOR

       Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT

       Copyright (C) 2009, 2010, 2011, 2012, 2013 Andrew Main (Zefram) <zefram@fysh.org>

LICENSE

       This module is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.