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autobox(3)	      User Contributed Perl Documentation	    autobox(3)

       autobox - call methods on native	types

	   use autobox;

	   # integers

	       my $range = 10->to(1); #	[ 10, 9, 8, 7, 6, 5, 4,	3, 2, 1	]

	   # floats

	       my $error = 3.1415927->minus(22/7)->abs();

	   # strings

	       my @list	= 'SELECT * FROM foo'->list();
	       my $greeting = "Hello, world!"->upper();	# "HELLO, WORLD!"


	   # arrays and	array refs

	       my $schwartzian = @_->map(...)->sort(...)->map(...);
	       my $hash	= [ 'SELECT * FROM foo WHERE id	IN (?, ?)', 1, 2 ]->hash();

	   # hashes and	hash refs

	       { alpha => 'beta', gamma	=> 'vlissides' }->for_each(...);

	   # code refs

	       my $plus_five = (\&add)->curry()->(5);
	       my $minus_three = sub { $_[0] - $_[1] }->reverse->curry->(3);

	   # can, isa, VERSION,	import and unimport can	be accessed via	autobox_class

	       say []->autobox_class->VERSION

       The "autobox" pragma allows methods to be called	on integers, floats,
       strings,	arrays,	hashes,	and code references in exactly the same	manner
       as blessed references.

       Autoboxing is transparent: values are not blessed into their (user-
       defined)	implementation class (unless the method	elects to bestow such
       a blessing) - they simply use its methods as though they	are.

       The classes (packages) into which the native types are boxed are	fully
       configurable.  By default, a method invoked on a	non-object value is
       assumed to be defined in	a class	whose name corresponds to the "ref()"
       type of that value - or SCALAR if the value is a	non-reference.

       This mapping can	be overridden by passing key/value pairs to the	"use
       autobox"	statement, in which the	keys represent native types, and the
       values their associated classes.

       As with regular objects,	autoboxed values are passed as the first
       argument	of the specified method.  Consequently,	given a	vanilla	"use

	   "Hello, world!"->upper()

       is invoked as:

	   SCALAR::upper("hello, world!")


	   [ 1 .. 10 ]->for_each(sub { ... })

       resolves	to:

	   ARRAY::for_each([ 1 .. 10 ],	sub { ... })

       Values beginning	with the array "@" and hash "%"	sigils are passed by
       reference, i.e. under the default bindings:

	   @array->join(', ')
	   @{ ... }->length()

       are equivalent to:

	   ARRAY::join(\@array,	', ')
	   ARRAY::length(\@{ ... })

       Multiple	"use autobox" statements can appear in the same	scope. These
       are merged both "horizontally" (i.e.  multiple classes can be
       associated with a particular type) and "vertically" (i.e. multiple
       classes can be associated with multiple types).


	   use autobox SCALAR => 'Foo';
	   use autobox SCALAR => 'Bar';

       - associates SCALAR types with a	synthetic class	whose @ISA includes
       both "Foo" and "Bar" (in	that order).


	   use autobox SCALAR => 'Foo';
	   use autobox SCALAR => 'Bar';
	   use autobox ARRAY  => 'Baz';


	   use autobox SCALAR => [ 'Foo', 'Bar'	];
	   use autobox ARRAY  => 'Baz';

       - bind SCALAR types to the "Foo"	and "Bar" classes and ARRAY types to

       "autobox" is lexically scoped, and bindings for an outer	scope can be
       extended	or countermanded in a nested scope:

	       use autobox; # default bindings:	autobox	all native types

		   # appends 'MyScalar'	to the @ISA associated with SCALAR types
		   use autobox SCALAR => 'MyScalar';

	       # back to the default (no MyScalar)

       Autoboxing can be turned	off entirely by	using the "no" syntax:

	       use autobox;
	       no autobox;

       - or can	be selectively disabled	by passing arguments to	the "no
       autobox"	statement:

	   use autobox;	# default bindings

	   no autobox qw(SCALAR);

	   []->foo(); #	OK: ARRAY::foo([])

	   "Hello, world!"->bar(); # runtime error

       Autoboxing is not performed for barewords i.e.

	   my $foo = Foo->new();


	   my $foo = new Foo;

       behave as expected.

       Methods are called on native types by means of the arrow	operator. As
       with regular objects, the right hand side of the	operator can either be
       a bare method name or a variable	containing a method name or subroutine
       reference. Thus the following are all valid:

	   sub method1 { ... }
	   my $method2 = 'some_method';
	   my $method3 = sub { ... };
	   my $method4 = \&some_method;

	   " ... "->method1();
	   [ ... ]->$method2();
	   { ... }->$method3();
	   sub { ... }->$method4();

       A native	type is	only associated	with a class if	the type => class
       mapping is supplied in the "use autobox"	statement. Thus	the following
       will not	work:

	   use autobox SCALAR => 'MyScalar';


       - as no class is	specified for the ARRAY	type. Note: the	result of
       calling a method	on a native type that is not associated	with a class
       is the usual runtime error message:

	   Can't call method "some_array_method" on unblessed reference	at ...

       As a convenience, there is one exception	to this	rule. If "use autobox"
       is invoked with no arguments (ignoring the DEBUG	option)	the four main
       native types are	associated with	classes	of the same name.


	   use autobox;

       - is equivalent to:

	   use autobox
	       SCALAR => 'SCALAR',
	       ARRAY  => 'ARRAY',
	       HASH   => 'HASH',
	       CODE   => 'CODE';

       This facilitates	one-liners and prototypes:

	   use autobox;

	   sub SCALAR::split { [ split '', $_[0] ] }
	   sub ARRAY::length { scalar @{$_[0]} }

	   print "Hello, world!"->split->length();

       However,	using these default bindings is	not recommended	as there's no
       guarantee that another piece of code won't trample over the same

       A mapping from native types to their user-defined classes can be
       specified by passing a hashref or a list	of key/value pairs to the "use
       autobox"	statement.

       The following example shows the range of	valid arguments:

	   use autobox {
	       SCALAR	 => 'MyScalar'			   # class name
	       ARRAY	 => 'MyNamespace::',		   # class prefix (ending in '::')
	       HASH	 => [ 'MyHash',	'MyNamespace::'	], # one or more class names and/or prefixes
	       CODE	 => ...,			   # any of the	3 value	types above
	       INTEGER	 => ...,			   # any of the	3 value	types above
	       FLOAT	 => ...,			   # any of the	3 value	types above
	       NUMBER	 => ...,			   # any of the	3 value	types above
	       STRING	 => ...,			   # any of the	3 value	types above
	       UNDEF	 => ...,			   # any of the	3 value	types above
	       UNIVERSAL => ...,			   # any of the	3 value	types above
	       DEFAULT	 => ...,			   # any of the	3 value	types above
	       DEBUG	 => ...				   # boolean or	coderef

       DEFAULT and UNIVERSAL options can take three different types of value:

       o   A class name	e.g.

	       use autobox INTEGER => 'MyInt';

	   This	binds the specified native type	to the specified class.	All
	   methods invoked on literals or values of type "key" will be
	   dispatched as methods of the	class specified	in the corresponding

       o   A namespace:	this is	a class	prefix (up to and including the	final
	   '::') to which the specified	type name (INTEGER, FLOAT, STRING &c.)
	   will	be appended:


	       use autobox ARRAY => 'Prelude::';

	   is equivalent to:

	       use autobox ARRAY => 'Prelude::ARRAY';

       o   A reference to an array of class names and/or namespaces. This
	   associates multiple classes with the	specified type.

       The "DEFAULT" option specifies bindings for any of the four default
       types (SCALAR, ARRAY, HASH and CODE) not	supplied in the	"use autobox"
       statement. As with the other options, the "value" corresponding to the
       "DEFAULT" "key" can be a	class name, a namespace, or a reference	to an
       array containing	one or more class names	and/or namespaces.


	   use autobox
	       STRING  => 'MyString',
	       DEFAULT => 'MyDefault';

       is equivalent to:

	   use autobox
	       STRING  => 'MyString',
	       SCALAR  => 'MyDefault',
	       ARRAY   => 'MyDefault',
	       HASH    => 'MyDefault',
	       CODE    => 'MyDefault';

       Which in	turn is	equivalent to:

	   use autobox
	       INTEGER => 'MyDefault',
	       FLOAT   => 'MyDefault',
	       STRING  => [ 'MyString',	'MyDefault' ],
	       ARRAY   => 'MyDefault',
	       HASH    => 'MyDefault',
	       CODE    => 'MyDefault';

       Namespaces in DEFAULT values have the default type name appended,
       which, in the case of defaulted SCALAR types, is	SCALAR rather than
       INTEGER,	FLOAT &c.


	   use autobox
	       ARRAY   => 'MyArray',
	       HASH    => 'MyHash',
	       CODE    => 'MyCode',
	       DEFAULT => 'MyNamespace::';

       is equivalent to:

	   use autobox
	       INTEGER => 'MyNamespace::SCALAR',
	       FLOAT   => 'MyNamespace::SCALAR',
	       STRING  => 'MyNamespace::SCALAR',
	       ARRAY   => 'MyArray',
	       HASH    => 'MyArray',
	       CODE    => 'MyCode';

       Any of the four default types can be exempted from defaulting to	the
       DEFAULT value by	supplying a value of undef:

	   use autobox
	       HASH    => undef,
	       DEFAULT => 'MyDefault';

	   42->foo # ok: MyDefault::foo
	   []->bar # ok: MyDefault::bar

	   %INC->baz # not ok: runtime error

       The pseudotype, UNDEF, can be used to autobox undefined values. These
       are not autoboxed by default.

       This doesn't work:

	   use autobox;

	   undef->foo()	# runtime error

       This works:

	   use autobox UNDEF =>	'MyUndef';

	   undef->foo(); # ok

       So does this:

	   use autobox UNDEF =>	'MyNamespace::';

	   undef->foo(); # ok

       The virtual types NUMBER, SCALAR	and UNIVERSAL function as macros or
       shortcuts which create bindings for their subtypes. The type hierarchy
       is as follows:

		    +- SCALAR -+
		    |	       |
		    |	       +- NUMBER -+
		    |	       |	  |
		    |	       |	  +- INTEGER
		    |	       |	  |
		    |	       |	  +- FLOAT
		    |	       |
		    |	       +- STRING
		    +- ARRAY
		    +- HASH
		    +- CODE


	   use autobox NUMBER => 'MyNumber';

       is equivalent to:

	   use autobox
	       INTEGER => 'MyNumber',
	       FLOAT   => 'MyNumber';


	   use autobox SCALAR => 'MyScalar';

       is equivalent to:

	   use autobox
	       INTEGER => 'MyScalar',
	       FLOAT   => 'MyScalar',
	       STRING  => 'MyScalar';

       Virtual types can also be passed	to "unimport" via the "no autobox"
       syntax. This disables autoboxing	for the	corresponding subtypes e.g.

	   no autobox qw(NUMBER);

       is equivalent to:

	   no autobox qw(INTEGER FLOAT);

       Virtual type bindings can be mixed with ordinary	bindings to provide
       fine-grained control over inheritance and delegation. For instance:

	   use autobox
	       INTEGER => 'MyInteger',
	       NUMBER  => 'MyNumber',
	       SCALAR  => 'MyScalar';

       would result in the following bindings:

	   42->foo	       -> [ MyInteger, MyNumber, MyScalar ]
	   3.1415927->bar      -> [ MyNumber, MyScalar ]
	   "Hello, world!->baz -> [ MyScalar ]

       Note that DEFAULT bindings take precedence over virtual type bindings

	   use autobox
	       UNIVERSAL => 'MyUniversal',
	       DEFAULT	 => 'MyDefault'; # default SCALAR, ARRAY, HASH and CODE	before UNIVERSAL

       is equivalent to:

	 use autobox
	     INTEGER =>	[ 'MyDefault', 'MyUniversal' ],
	     FLOAT   =>	[ 'MyDefault', 'MyUniversal' ],	# ... &c.

       "DEBUG" exposes the current bindings for	the scope in which "use
       autobox"	is called by means of a	callback, or a static debugging

       This allows the computed	bindings to be seen in "longhand".

       The option is ignored if	the value corresponding	to the "DEBUG" key is

       If the value is a CODE ref, then	this sub is called with	a reference to
       the hash	containing the computed	bindings for the current scope.

       Finally,	if "DEBUG" is true but not a CODE ref, the bindings are	dumped
       to STDERR.


	   use autobox DEBUG =>	1, ...


	   use autobox DEBUG =>	sub { ... }, ...


	   sub my_callback ($) {
	       my $hashref = shift;

	   use autobox DEBUG =>	\&my_callback, ...

       This method sets	up "autobox" bindings for the current lexical scope.
       It can be used to implement "autobox" extensions	i.e. lexically-scoped
       modules that provide "autobox" bindings for one or more native types
       without requiring calling code to "use autobox".

       This is done by subclassing "autobox" and overriding "import". This
       allows extensions to effectively	translate "use MyModule" into a
       bespoke "use autobox" call. e.g.:

	   package String::Trim;

	   use base qw(autobox);

	   sub import {
	       my $class = shift;
		   STRING => 'String::Trim::String'

	   package String::Trim::String;

	   sub trim {
	       my $string = shift;
	       $string =~ s/^\s+//;
	       $string =~ s/\s+$//;


       Note that "trim"	is defined in an auxiliary class rather	than in
       "String::Trim" itself to	prevent	"String::Trim"'s own methods (i.e. the
       methods it inherits from	"autobox") being exposed to "STRING" types.

       This module can now be used without a "use autobox" statement to	enable
       the "trim" method in the	current	lexical	scope. e.g.:

	   #!/usr/bin/env perl

	   use String::Trim;

	   print "  Hello, world!  "->trim();

       "autobox" adds a	single method to all autoboxed types: "autobox_class".
       This can	be used	to call	"can", "isa", "VERSION", "import" and
       "unimport". e.g.

	   if (sub { ... }->autobox_class->can('curry')) ...
	   if (42->autobox_class->isa('SCALAR')) ...

       Note: "autobox_class" should always be used when	calling	these methods.
       The behaviour when these	methods	are called directly on the native type


       - is undefined.

       "autobox" includes an additional	module,	"autobox::universal", which
       exports a single	subroutine, "type".

       This sub	returns	the type of its	argument within	"autobox" (which is
       essentially longhand for	the type names used within perl). This value
       is used by "autobox" to associate a method invocant with	its designated
       classes.	e.g.

	   use autobox::universal qw(type);

	   type("42")  # STRING
	   type(42)    # INTEGER
	   type(42.0)  # FLOAT
	   type(undef) # UNDEF

       "autobox::universal" is loaded automatically by "autobox", and, as its
       name suggests, can be used to install a universal "type"	method for
       autoboxed values	e.g.

	   use autobox UNIVERSAL => 'autobox::universal';

	   42->type	   # INTEGER
	   3.1415927->type # FLOAT
	   %ENV->type	   # HASH


	   "Hello, world!"->length()

       is slightly slower than the equivalent method call on a string-like
       object, and significantly slower	than

	   length("Hello, world!")


       Due to Perl's precedence	rules, some autoboxed literals may need	to be

       For instance, while this	works:

	   my $curried = sub { ... }->curry();

       this doesn't:

	   my $curried = \&foo->curry();

       The solution is to wrap the reference in	parentheses:

	   my $curried = (\&foo)->curry();

       The same	applies	for signed integer and float literals:

	   # this works
	   my $range = 10->to(1);

	   # this doesn't work
	   my $range = -10->to(10);

	   # this works
	   my $range = (-10)->to(10);

       print BLOCK

       Perl's special-casing for the "print BLOCK ..." syntax (see perlsub)
       means that "print { expression()	} ..."	(where the curly brackets
       denote an anonymous HASH	ref) may require some further disambiguation:

	   # this works
	   print { foo => 'bar'	}->foo();

	   # and this
	   print { 'foo', 'bar'	}->foo();

	   # and even this
	   print { 'foo', 'bar', @_ }->foo();

	   # but this doesn't
	   print { @_ }->foo() ? 1 : 0

       In the latter case, the solution	is to supply something other than a
       HASH ref	literal	as the first argument to "print()":

	   # e.g.
	   print STDOUT	{ @_ }->foo() ?	1 : 0;

	   # or
	   my $hashref = { @_ };
	   print $hashref->foo() ? 1 : 0;

	   # or
	   print '', { @_ }->foo() ? 1 : 0;

	   # or
	   print '' . {	@_ }->foo() ? 1	: 0;

	   # or	even
	   { @_	}->print_if_foo(1, 0);

       eval EXPR

       Like most pragmas, "autobox" performs operations	at compile time, and,
       as a result, runtime string "eval"s are not executed within its scope
       i.e. this doesn't work:

	   use autobox;

	   eval	"42->foo";

       The workaround is to use	"autobox" within the "eval" e.g.

	   eval	<<'EOS';
	       use autobox;

       Note that the "eval BLOCK" form works as	expected:

	   use autobox;

	   eval	{ 42->foo() }; # OK


       o   autobox::Core

       o   Moose::Autobox

       o   perl5i

       o   Scalar::Properties

       chocolateboy <>

       Copyright (c) 2003-2016,	chocolateboy.

       This module is free software. It	may be used, redistributed and/or
       modified	under the same terms as	Perl itself.

perl v5.24.1			  2016-08-26			    autobox(3)


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