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() and isa() work as expected

    if ("Hello, world!"->can('foo')) ...
    if (3.1415927->isa('SCALAR')) ...

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 overriden 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. mutiple classes can be associated with a particular type) and "vertically" (i.e. a previously unboxed type can be associated with a class).

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
    DEFAULT => ...,                           # any of the 3 value types above
    DEBUG   => ...;                           # boolean or coderef

The INTEGER, FLOAT, NUMBER, STRING, SCALAR, ARRAY, HASH, CODE, UNDEF and DEFAULT keys 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'.

If a class name is supplied for DEFAULT, it becomes the default class for all unspecified cases for that invocation of use autobox. Thus:
```
use autobox
    STRING  => 'MyString',
    DEFAULT => 'MyDefault';
```
- will invoke STRING methods on MyString and all other methods on MyDefault.
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::';
```
binds ARRAY types to the Prelude::ARRAY class.

As with the class name form, specifying a default namespace e.g.
```
use autobox
    FLOAT   => 'MyFloat',
    DEFAULT => 'MyNamespace::';
```
binds MyNamespace::ARRAY, MyNamespace::HASH &c. to the corresponding types.
A reference to an array of class names and/or namespaces. This associates multiple classes with the specified type.

Virtual Types

Rather than representing native types, the NUMBER and SCALAR options function as macros or shortcuts which create bindings for their scalar subtypes (INTEGER, FLOAT and STRING).

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';

Bindings for subtypes that are created in this way are automatically deleted when no autobox is called with the corresponding virtual type. Thus:

no autobox qw(NUMBER);

is equivalent to:

no autobox qw(INTEGER FLOAT);

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

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

would result in the methods on the left being looked up (in order) in the classes on the right:

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

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 => 'MyClass'; 

undef->foo(); # ok

So does this:

use autobox UNDEF => 'MyNamespace::'; 

undef->foo(); # ok

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

On its own, autobox doesn't implement any methods that can be called on native types. However, it does implement two methods that subclasses can override to provide autobox extensions i.e. bundles of methods for one or more native types. These can be composed both "horizontally" (multiple classes for the same type) and "vertically" (multiple classes for different types).

import

The simplest way to implement an autobox extension is to inherit from autobox and override import. This allows subclasses 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(SCALAR => '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 auxilliary 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.

Clients can now use this module to enable the trim method in the current lexical scope. e.g.:

use String::Trim;

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

defaults

For more exotic wrappers, autobox implements a defaults method that returns a HASH ref that defines the module's default bindings.

package Prelude;

use base qw(autobox);

sub defaults {
    my $class = shift;

    return {
        SCALAR  => 'Foo::Scalar',
        ARRAY   => 'Bar::Array',
        HASH    => [ qw(Baz::Hash Quux::Hash) ],
        UNDEF   => undef,
        DEFAULT => undef
    };
}

1;

The HASH ref returned by the defaults method serves three purposes.

its keys constrain the valid keys that can be supplied to the use Prelude statement. In the above example,
```
use Prelude CODE => 'MyCode';
```
would trigger a compile-time error as CODE is not is not included in the default keys.
it can define a DEFAULT binding for all types omitted from the use Prelude statement.

it specifies the default bindings when use Prelude is called with no arguments. e.g.:

use Prelude;

and

use Prelude DEBUG => 1;

are equivalent to:

use autobox
    SCALAR => 'Foo::Scalar',
    ARRAY  => 'Bar::Array',
    HASH   => [ qw(Baz::Hash Quux::Hash) ];

The defaults method can also be used to enable autoboxing for new types such as LVALUEs, GLOBs, or VSTRINGs.

type

This method 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.

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

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);

UNIVERSAL

Although can and isa are "overloaded" for autoboxed values, the VERSION method isn't. Thus, while these work:

[ ... ]->can('pop')

3.1415->isa('MyScalar')

This doesn't:

use MyScalar 1.23;

use autobox SCALAR => MyScalar;

print "Hello, world!"->VERSION(), $/;

Though, of course:

print MyScalar->VERSION(), $/;

and

print $MyScalar::VERSION, $/;

continue to work.

Likewise, import and unimport are unaffected by the autobox pragma:

# equivalent to Foo->import() rather than MyScalar->import('Foo')
'Foo'->import()

# error: Can't call method "import" on unblessed reference
[]->import()

autobox

eval EXPR

Like most pragmas autobox performs some of its 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

2.52

AUTHOR

chocolateboy <chocolate.boy@email.com>

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

Virtual Types

UNDEF

DEBUG

METHODS

import

defaults

type

CAVEATS

Performance

Gotchas

Precedence

print BLOCK

UNIVERSAL

eval EXPR

VERSION

SEE ALSO

AUTHOR

COPYRIGHT

Module Install Instructions