Provided by: libautobox-perl_2.85-1build2_amd64 
NAME
autobox - call methods on native types
SYNOPSIS
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!"
$greeting->for_each(\&character_handler);
# 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(...);
%hash->keys();
# code refs
my $plus_five = (\&add)->curry()->(5);
my $minus_three = sub { $_[0] - $_[1] }->reverse->curry->(3);
# can, isa, VERSION, import and unimport can be accessed via autobox_class
42->autobox_class->isa('MyNumber')
say []->autobox_class->VERSION
DESCRIPTION
The "autobox" pragma allows methods to be called on integers, floats, strings, arrays,
hashes, and code references in exactly the same manner as blessed references.
Autoboxing is transparent: values are not blessed into their (user-defined) implementation
class (unless the method elects to bestow such a blessing) - they simply use its methods
as though they are.
The classes (packages) into which the native types are boxed are fully configurable. By
default, a method invoked on a non-object value is assumed to be defined in a class whose
name corresponds to the "ref()" type of that value - or SCALAR if the value is a non-
reference.
This mapping can be overridden by passing key/value pairs to the "use autobox" statement,
in which the keys represent native types, and the values their associated classes.
As with regular objects, autoboxed values are passed as the first argument of the
specified method. Consequently, given a vanilla "use autobox":
"Hello, world!"->upper()
is invoked as:
SCALAR::upper("hello, world!")
while:
[ 1 .. 10 ]->for_each(sub { ... })
resolves to:
ARRAY::for_each([ 1 .. 10 ], sub { ... })
Values beginning with the array "@" and hash "%" sigils are passed by reference, i.e.
under the default bindings:
@array->join(', ')
@{ ... }->length()
%hash->keys()
%$hash->values()
are equivalent to:
ARRAY::join(\@array, ', ')
ARRAY::length(\@{ ... })
HASH::keys(\%hash)
HASH::values(\%$hash)
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).
Thus:
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).
Likewise:
use autobox SCALAR => 'Foo';
use autobox SCALAR => 'Bar';
use autobox ARRAY => 'Baz';
and
use autobox SCALAR => [ 'Foo', 'Bar' ];
use autobox ARRAY => 'Baz';
- bind SCALAR types to the "Foo" and "Bar" classes and ARRAY types to "Baz".
"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();
and:
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';
@array->some_array_method();
- 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.
Thus:
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 namespace/methods.
OPTIONS
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
};
The INTEGER, FLOAT, NUMBER, STRING, SCALAR, ARRAY, HASH, CODE, UNDEF, DEFAULT and
UNIVERSAL options can take three different types of value:
• A class name e.g.
use autobox INTEGER => 'MyInt';
This binds the specified native type to the specified class. All methods invoked on
values of type "key" will be dispatched as methods of the class specified in the
corresponding "value".
• 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:
Thus:
use autobox ARRAY => 'Prelude::';
is equivalent to:
use autobox ARRAY => 'Prelude::ARRAY';
• A reference to an array of class names and/or namespaces. This associates multiple
classes with the specified type.
DEFAULT
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.
Thus:
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.
Thus:
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
UNDEF
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
NUMBER, SCALAR and UNIVERSAL
The virtual types NUMBER, SCALAR and UNIVERSAL function as macros or shortcuts which
create bindings for their subtypes. The type hierarchy is as follows:
UNIVERSAL -+
|
+- SCALAR -+
| |
| +- NUMBER -+
| | |
| | +- INTEGER
| | |
| | +- FLOAT
| |
| +- STRING
|
+- ARRAY
|
+- HASH
|
+- CODE
Thus:
use autobox NUMBER => 'MyNumber';
is equivalent to:
use autobox
INTEGER => 'MyNumber',
FLOAT => 'MyNumber';
And:
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 i.e.
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
"DEBUG" exposes the current bindings for the scope in which "use autobox" is called by
means of a callback, or a static debugging function.
This allows the computed bindings to be seen in "longhand".
The option is ignored if the value corresponding to the "DEBUG" key is false.
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.
Thus:
use autobox DEBUG => 1, ...
or
use autobox DEBUG => sub { ... }, ...
or
sub my_callback ($) {
my $hashref = shift;
...
}
use autobox DEBUG => \&my_callback, ...
METHODS
import
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;
$class->SUPER::import(
STRING => 'String::Trim::String'
);
}
package String::Trim::String;
sub trim {
my $string = shift;
$string =~ s/^\s+//;
$string =~ s/\s+$//;
$string;
}
1;
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();
UNIVERSAL METHODS FOR AUTOBOXED TYPES
autobox_class
"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 e.g.:
42->can('foo')
42->isa('Bar')
42->VERSION
- is undefined.
EXPORTS
type
"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
CAVEATS
Performance
Calling
"Hello, world!"->length()
is slightly slower than the equivalent method call on a string-like object, and
significantly slower than
length("Hello, world!")
Gotchas
Precedence
Due to Perl's precedence rules, some autoboxed literals may need to be parenthesized:
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;
42->foo();
EOS
Note that the "eval BLOCK" form works as expected:
use autobox;
eval { 42->foo() }; # OK
VERSION
2.85
SEE ALSO
• autobox::Core
• Moose::Autobox
• perl5i
• Scalar::Properties
AUTHOR
chocolateboy <chocolate@cpan.org>
COPYRIGHT
Copyright (c) 2003-2017, chocolateboy.
This module is free software. It may be used, redistributed and/or modified under the same
terms as Perl itself.