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.