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.

The autoboxing is transparent: boxed 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 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 asociated 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 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 literals or 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, ...

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

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

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

METHODS

import

On its own, autobox doesn't implement any methods that can be called on native types. However, its static method, import, 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::Scalar');
}

package String::Trim::Scalar;

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 SCALAR 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();

EXPORTS

autobox_class

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

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

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("Hello, world!") # STRING
type(42)              # INTEGER
type([])              # ARRAY
type(sub { })         # CODE

autobox::universal is loaded automatically by autobox, and, as its name suggests, can be used to install a universal method (i.e. a method for all autobox types) e.g.

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

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

CAVEATS

Performance

Autoboxing comes at a price. 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 evals 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

2.75

AUTHOR

chocolateboy <chocolate@cpan.org>

COPYRIGHT

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

To install autobox, copy and paste the appropriate command in to your terminal.

cpanm

cpanm autobox

CPAN shell

perl -MCPAN -e shell
install autobox

For more information on module installation, please visit the detailed CPAN module installation guide.

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NAME

SYNOPSIS

DESCRIPTION

OPTIONS

DEFAULT

UNDEF

NUMBER, SCALAR and UNIVERSAL

DEBUG

METHODS

import

EXPORTS

autobox_class

type

CAVEATS

Performance

Gotchas

Precedence

print BLOCK

eval EXPR

VERSION

SEE ALSO

AUTHOR

COPYRIGHT

Module Install Instructions