NAME
autobox::Core - Core functions exposed as methods in primitive types
SYNOPSIS
use autobox::Core;
"Hello, World\n"->uc->print;
DESCRIPTION
The autobox module lets you call methods on primitive datatypes such as
scalars and arrays.
autobox::CORE defines methods for core operations such as "join",
"print", most everything in perlfunc, some things from Scalar::Util and
List::Util, and some Perl 5 versions of methods taken from Perl 6.
These methods expose as methods the built-in functions for minipulating
numbers, strings, arrays, hashes, and code references.
It can be handy to use built-in functions as methods to avoid messy
dereferencing syntaxes and parentheses pile ups.
autobox::Core is what you'd call a *stub* module. It is mostly glue,
presenting existing functions with a new interface. Most of the methods
read like "sub hex ($) { hex($_[0]) }". Besides built-ins that operate
on hashes, arrays, scalars, and code references, some Perl 6-ish things
were thrown in, and some keyword like "foreach" have been turned into
methods.
What's Implemented?
All of the functions listed in perldoc under the headings: "Functions
for real @ARRAYs", "Functions for real %HASHes", "Functions for list
data", and "Functions for SCALARs or strings", plus a few taken from
other sections and documented below. Methods from Scalar::Util and
List::Util were thrown in. Some things expected in Perl 6, such as
"last" ("last_idx"), "elems", and "curry", have been thrown in.
"flatten" explicitly flattens an array. Functions such as "add" have
been defined for numeric operations.
Here's a small sample:
print [10, 20, 30, 40, 50]->pop, "\n";
print [10, 20, 30, 40, 50]->shift, "\n";
my $arrref = [10, 20, 30];
my $lala;
$lala = "Lalalalala\n"; print "chomp: ", $lala->chomp, ' ', $lala, "\n";
$lala = "Lalalalala\n"; print "lcfirst: ", $lala->lcfirst, ' ', $lala, "\n";
my $hashref = { foo => 10, bar => 20, baz => 30, qux => 40 };
print "hash keys: ", $hashref->keys->join(' '), "\n"; # or if you prefer...
print "hash keys: ", join ' ', $hashref->keys(), "\n";
Of the built-in stuff, only a few stragglers such as "srand" were
excluded.
Scalar String Related Methods
"concat" is the "." operator.
"strip" is not a built-in operator or function but is instead one of a
number of user-defined convinience methods. "strip" strips out
whitespace from the beginning and end of a string. This is redundant and
subtely different from "trim" XXX.
"trim" strips out whitespace from the beginning and end of a string.
"title_case", "center", "ltrim", "rtrim", and "trim" were taken from
perl5i.
"split" is called on a non-reference scalar with the regular expression
passed in. This is done for consistency with "m" and "s".
print "10, 20, 30, 40"->split(qr{, ?})->elements, "\n";
"chomp", "chop", "chr", "crypt", "index", "lc", "lcfirst", "length",
"ord", "pack", "reverse", "rindex", "sprintf", "substr", "uc",
"ucfirst", "unpack", "quotemeta", "vec", "undef", "m", "nm", "s",
"split". "eval", "system", and "backtick".
"nm" corresponds to "!~".
"m" is "m//". "$foo->m(/bar/)" corresponds to "$foo =~ m/bar/". "s" is
"s///". To use "m" and "s", pass a regular expression created with
"qr//" and specify its flags as part of the regular expression using the
"(?imsx-imsx)" syntax documented in perlre. "m" returns an array
reference so that things such as "map" and "grep" may be called on the
result.
my ($street_number, $street_name, $apartment_number) =
"1234 Robin Drive #101"->m(qr{(\d+) (.*)(?: #(\d+))?})->elements;
print "$street_number $street_name $apartment_number\n";
"undef" assigns "undef" to the value. It is not a test. XXX for some
reason, there's no "defined".
center()
my $centered_string = $string->center($length);
my $centered_string = $string->center($length, $character);
Centers $string between $character. $centered_string will be of length
$length.
$character defaults to " ".
say "Hello"->center(10); # " Hello ";
say "Hello"->center(10, '-'); # "---Hello--";
"center()" will never truncate $string. If $length is less than
"$string->length" it will just return $string.
say "Hello"->center(4); # "Hello";
I/O
"print" and "say".
Number Related Methods
"abs", "atan2", "cos", "exp", "int", "log", "oct", "hex", "rand", "sin",
and "sqrt" are named after the built-in functions of the same name.
Operators were given names as follows: "add", "and", "band", "bor",
"bxor", "cmp", "dec", "div", "eq", "flip", "ge", "gt", "inc", "le",
"lshift", "lt", "mod", "mult", "mcmp", "ne", "neg", "meq", "mge", "mgt",
"mle", "mlt", "mne", "not", "or", "pow", "rpt", "rshift", "sub", "xor".
"flip" is "~" which is the binary (rather than boolean) "not".
"lshift" is "<<" and "rshift" is ">>".
"mge" is ">=". "<mle"> is "<=". I'm not sure where the "m" came from.
"sub" is subtract, I think, but it should not be named the same as the
anonymous subroutine constructor XXX.
is_number
$is_a_number = $thing->is_number;
Returns true if $thing is a number understood by Perl.
12.34->is_number; # true
"12.34"->is_number; # also true
is_positive
$is_positive = $thing->is_positive;
Returns true if $thing is a positive number.
0 is not positive.
is_negative
$is_negative = $thing->is_negative;
Returns true if $thing is a negative number.
0 is not negative.
is_integer
$is_an_integer = $thing->is_integer;
Returns true if $thing is an integer.
12->is_integer; # true
12.34->is_integer; # false
is_int
A synonym for is_integer
is_decimal
$is_a_decimal_number = $thing->is_decimal;
Returns true if $thing is a decimal number.
12->is_decimal; # false
12.34->is_decimal; # true
".34"->is_decimal; # true
That's it.
Reference Related Methods
Besides the "Functions for SCALARs" section of perlfunc, the following
were implemented, where they make sense: "tie", "tied", "ref", "undef",
"bless", and "vec". "tie", "tied", and "undef" don't work on code
references, and "bless" doesn't work on non-reference scalars (okay,
that's no longer true). "quotemeta" works on non-reference scalars,
along with "split", "m", and "s" for regular expression operations.
"ref" is the same as the "ref" keyword in that it tells you what kind of
a reference something is if it's a reference; XXX there's currently no
counterpart to the "\" operator, which takes something and gives you a
reference to it.
Array Methods
Array methods work on both arrays and array references:
my $arr = [ 1 .. 10 ];
$arr->undef;
Or:
my @arr = [ 1 .. 10 ];
@arr->undef;
Arrays can tell you how many elements they contain and the index of
their last element:
my $arr = [ 1 .. 10 ];
print '$arr contains ', $arr->size,
' elements, the last having an index of ', $arr->last_index, "\n";
Array references have a "flatten" method to dump their elements. This is
the same as "@{$array_ref}".
my $arr = [ 1 .. 10 ];
print join ' -- ', $arr->flatten, "\n";
List context forces methods to return a list:
my @arr = ( 1 .. 10 );
print join ' -- ', @arr->grep(sub { $_ > 3 }), "\n";
Methods may be chained; scalar context forces methods to return a
reference:
my @arr = ( 1 .. 10 );
print @arr->grep(sub { $_ > 3 })->min, "\n";
Arrays can be iterated on using "for" and "foreach". Both take a code
reference as the body of the for statement. "foreach" passes the current
element itself in each pass. "for" passes the index of the current
element in to that code block, and then the current element, and then a
reference to the array itself.
my $arr = [ 1 .. 10 ];
$arr->foreach(sub { print $_[0], "\n" });
$arr->for(sub { die unless $_[1] == $_[2]->[$_[0]] });
"sum" is a toy poke at doing Language::Functional-like stuff:
print $arrref->sum, "\n";
Methods for array creation: "to", "upto", and "downto".
1->to(5); # creates [1, 2, 3, 4, 5]
1->upto(5); # creates [1, 2, 3, 4, 5]
5->downto(5); # creates [5, 4, 3, 2, 1]
These wrap the ".." operator.
$arr->first(sub { /5/ });
head
my $first = @list->head;
Returns the first element from @list.
tail
my @list = qw(foo bar baz quux);
my @rest = @list->tail; # [ 'bar', 'baz', 'quux' ]
Returns all but the first element from @list. In scalar context returns
an array reference.
Optionally, you can pass a number as argument to ask for the last $n
elements:
@rest = @list->tail(2); # [ 'baz', 'quux' ]
slice
my @sublist = @list->slice(@indexes);
Returns a list containing the elements from @list at the indices
@indices. In scalar context, returns an array reference.
range
my @sublist = @list->range( $lower_idx, $upper_idx );
Returns a list containing the elements from @list with indices ranging
from $lower_idx to $upper_idx. Returns an array reference in scalar
context.
last_index
my $last_index = @array->last_index
Returns @array's last index. Optionally, takes a Coderef or a Regexp, in
which case it will return the index of the last element that matches
such regex or makes the code reference return true. Example:
my @things = qw(pear poll potato tomato);
my $last_p = @things->last_index(qr/^p/); # 2
first_index
my $first_index = @array->first_index; # 0
For simmetry, returns the first index of @array. If passed a Coderef or
Regexp, it will return the index of the first element that matches.
my @things = qw(pear poll potato tomato);
my $last_p = @things->first_index(qr/^t/); # 3
Hash Methods
"each" is like "foreach" but for hash references. For each key in the
hash, the code reference is invoked with the key and the corresponding
value as arguments:
my $hashref = { foo => 10, bar => 20, baz => 30, quux => 40 };
$hashref->each(sub { print $_[0], ' is ', $_[1], "\n" });
There is currently no way to have the elements sorted before they are
handed to the code block. If someone requests a way of passing in a sort
criteria, I'll implement it.
"slice" takes a list of hash keys and returns the corresponding values
e.g.
my %hash = (
one => 'two',
three => 'four',
five => 'six'
);
print %hash->slice(qw(one five))->join(' and '); # prints "two and six"
flip()
Exchanges values for keys in a hash.
my %things = ( foo => 1, bar => 2, baz => 5 );
my %flipped = %things->flip; # { 1 => foo, 2 => bar, 5 => baz }
If there is more than one occurence of a certain value, any one of the
keys may end up as the value. This is because of the random ordering of
hash keys.
# Could be { 1 => foo }, { 1 => bar }, or { 1 => baz }
{ foo => 1, bar => 1, baz => 1 }->flip;
Because hash references cannot usefully be keys, it will not work on
nested hashes.
{ foo => [ 'bar', 'baz' ] }->flip; # dies
Code Methods
You may "curry" code references:
$adding_up_numbers = sub {
my $first_number = shift;
my $second_number = shift;
return $first_number + $second_number;
};
my $adding_five_to_numbers = $adding_up_numbers->curry(5);
$adding_five_to_numbers->(20)->print; "\n"->print;
"times" executes a coderef a given number of times:
5->times(sub { print "hi\n"}); # XXX likely to change but it's in the code so bloody doc it so I have incentive to rethink it
XXX round this out
What's Missing?
Many operators. I'm tired. I'll do it in the morning. Maybe. Send me a
patch. Update: Someone sent me a patch for numeric operations.
File and socket operations are already implemented in an object-oriented
fashion care of IO::Handle, IO::Socket::INET, and IO::Any.
Functions listed in the perlfunc headings "System V interprocess
communication functions", "Fetching user and group info", "Fetching
network info", "Keywords related to perl modules", "Functions for
processes and process groups", "Keywords related to scoping",
"Time-related functions", "Keywords related to the control flow of your
perl program", "Functions for filehandles, files, or directories", and
"Input and output functions". These things are likely implemented in an
object oriented fashion by other CPAN modules, are keywords and not
functions, take no arguments, or don't make sense as part of the string,
number, array, hash, or code API. "srand" because you probably shouldn't
be using it.
"each" on hashes. There is no good reason it is missing. XXX.
Autoboxing
*This section quotes four pages from the manuscript of Perl 6 Now: The
Core Ideas Illustrated with Perl 5 by myself, Scott Walters. The text
appears in the book starting at page 248. This copy lacks the benefit of
copyedit - the finished product is of higher quality. See the shameless
plug in the SEE ALSO section for information on ordering Perl 6 Now.*
A *box* is an object that contains a primitive variable. Boxes are used
to endow primitive types with the capabilities of objects. This is
essential in strongly typed languages but never strictly required in
Perl. Programmers might write something like "my $number = Int->new(5)".
This is manual boxing. To *autobox* is to convert a simple type into an
object type automatically, or only conceptually. This is done by the
language. It makes a language look to programmers as if everything is an
object while the interpreter is free to implement data storage however
it pleases. Autoboxing is really making simple types such as numbers,
strings, and arrays appear to be objects.
"int", "num", "bit", "str", and other types with lower case names, are
primitives. They're fast to operate on, and require no more memory to
store than the data held strictly requires. "Int", "Num", "Bit", "Str",
and other types with an initial capital letter, are objects. These may
be subclassed (inherited from) and accept traits, among other things.
These objects are provided by the system for the sole purpose of
representing primitive types as objects, though this has many ancillary
benefits such as making "is" and "has" work. Perl provides "Int" to
encapsulate an "int", "Num" to encapsulate a "num", "Bit" to encapsulate
a "bit", and so on. As Perl's implementations of hashes and dynamically
expandable arrays store any type, not just objects, Perl programmers
almost never are required to box primitive types in objects. Perl's
power makes this feature less essential than it is in other languages.
ing makes primitive objects and they're boxed versions equivalent. An
"int" may be used as an "Int" with no constructor call, no passing,
nothing. This applies to constants too, not just variables:
# Perl 6 - autoboxing associates classes with primitives types:
print 4.sqrt, "\n";
This is perfectly valid Perl 6.
All of this applies to hashes and arrays, as well:
# Perl 6 - autoboxing associates classes with primitive types:
print [ 1 .. 20 ].elems, "\n";
The language is free to implement data storage however it wishes but the
programmer sees the variables as objects.
Expressions using autoboxing read somewhat like Latin suffixes. In the
autoboxing mind-set, you might not say that something is "made more
mnemonic", but has been "mnemonicified".
Autoboxing may be mixed with normal function calls. In the case where
the methods are available as functions and the functions are available
as methods, it is only a matter of personal taste how the expression
should be written:
# Calling methods on numbers and strings, these three lines are equivalent
# Perl 6
print sqrt 4;
print 4.sqrt;
4.sqrt.print;
The first of these three equivalents assumes that a global "sqrt()"
function exists. This first example would fail to operate if this global
function were removed and only a method in the "Num" package was left.
Perl 5 had the beginnings of autoboxing with filehandles:
use IO::Handle;
open my $file, '<', 'file.txt' or die $!;
$file->read(my $data, -s $file);
Here, "read" is a method on a filehandle we opened but *never blessed*.
This lets us say things like "$file->print(...)" rather than the often
ambagious
"print $file ...". To many people, much of the time, it makes more
conceptual sense as well.
Reasons to Box Primitive Types
What good is all of this?
Makes conceptual sense to programmers used to object interfaces as *the*
way to perform options.
Alternative idiom. Doesn't require the programmer to write or read
expressions with complex precedence rules or strange operators.
Many times that parenthesis would otherwise have to span a large
expression, the expression may be rewritten such that the parenthesis
span only a few primitive types.
Code may often be written with fewer temporary variables.
Autoboxing provides the benefits of boxed types without the memory bloat
of actually using objects to represent primitives. Autoboxing "fakes
it".
Strings, numbers, arrays, hashes, and so on, each have their own API.
Documentation for an "exists" method for arrays doesn't have to explain
how hashes are handled and vice versa.
Perl tries to accommodate the notion that the "subject" of a statement
should be the first thing on the line, and autoboxing furthers this
agenda.
Perl is an idiomatic language and this is an important idiom.
Subject First: An Aside
Perl's design philosophy promotes the idea that the language should be
flexible enough to allow programmers to place the of a statement first.
For example, "die $! unless read $file, 60" looks like the primary
purpose of the statement is to "die". While that might be the
programmers primary goal, when it isn't, the programmer can communicate
his real primary intention to programmers by reversing the order of
clauses while keeping the exact same logic: "read $file, 60 or die $!".
Autoboxing is another way of putting the subject first. Nouns make good
subjects, and in programming, variables, constants, and object names are
the nouns. Function and method names are verbs. "$noun->verb()" focuses
the readers attention on the thing being acted on rather than the action
being performed. Compare to "$verb($noun)".
Autoboxing and Method Results
In Chapter 11 [Subroutines], we had examples of ways an expression could
be written. Here it is again:
# Various ways to do the same thing:
print(reverse(sort(keys(%hash)))); # Perl 5 - pathological parenthetic
print reverse sort keys %hash; # Perl 5 - no unneeded parenthesis
print(reverse(sort(%hash,keys)))); # Perl 6 - pathological
print reverse sort %hash.keys; # Perl 6 - no unneeded parenthesis
%hash.keys ==> sort ==> reverse ==> print; # Perl 6 - pipeline operator
%hash.keys.sort.reverse.print; # Perl 6 - autobox
%hash->keys->sort->reverse->print; # Perl 5 - autobox
This section deals with the last two of these equivalents. These are
method calls use autobox::Core; use Perl6::Contexts;
my %hash = (foo => 'bar', baz => 'quux');
%hash->keys->sort->reverse->print; # Perl 5 - autobox
# prints "foo baz"
Each method call returns an array reference, in this example. Another
method call is immediately performed on this value. This feeding of the
next method call with the result of the previous call is the common mode
of use of autoboxing. Providing no other arguments to the method calls,
however, is not common.
Perl6::Contexts recognizes object context as provided by "->" and
coerces %hash and @array into references, suitable for use with autobox.
(Note that autobox also does this automatically as of version 2.40.)
autobox associates primitive types, such as references of various sorts,
with classes. autobox::Core throws into those classes methods wrapping
Perl's built-in functions. In the interest of full disclosure,
Perl6::Contexts and autobox::Core are my creations.
Autobox to Simplify Expressions
One of my pet peeves in programming is parenthesis that span large
expression. It seems like about the time I'm getting ready to close the
parenthesis I opened on the other side of the line, I realize that I've
forgotten something, and I have to arrow back over or grab the mouse.
When the expression is too long to fit on a single line, it gets broken
up, then I must decide how to indent it if it grows to 3 or more lines.
# Perl 5 - a somewhat complex expression
print join("\n", map { CGI::param($_) } @cgi_vars), "\n";
# Perl 5 - again, using autobox:
@cgi_vars->map(sub { CGI::param($_[0]) })->join("\n")->concat("\n")->print;
The autoboxed version isn't shorter, but it reads from left to right,
and the parenthesis from the "join()" don't span nearly as many
characters. The complex expression serving as the value being "join()"ed
in the non-autoboxed version becomes, in the autoboxed version, a value
to call the "join()" method on.
This "print" statement takes a list of CGI parameter names, reads the
values for each parameter, joins them together with newlines, and prints
them with a newline after the last one.
Pretending that this expression were much larger and it had to be broken
to span several lines, or pretending that comments are to be placed
after each part of the expression, you might reformat it as such:
@cgi_vars->map(sub { CGI::param($_[0]) }) # turn CGI arg names into values
->join("\n") # join with newlines
->concat("\n") # give it a trailing newline
->print; # print them all out
This could also have been written:
sub { CGI::param($_[0]) }->map(@cgi_vars) # turn CGI arg names into values
->join("\n") # join with newlines
->concat("\n") # give it a trailing newline
->print; # print them all out
"map()" is . The "map()" method defined in the "autobox::Core::CODE"
package takes for its arguments the things to map. The "map()" method
defined in the "autobox::Core::ARRAY" package takes for its argument a
code reference to apply to each element of the array.
*Here ends the text quoted from the Perl 6 Now manuscript.*
BUGS
Yes. Report them to the author,
[email protected]. The API is not yet
stable -- Perl 6-ish things and local extensions are still being
renamed.
HISTORY
See the Changes file.
COPYRIGHT AND LICENSE
Copyright (C) 2009, 2010 by Scott Walters and various contributors
listed (and unlisted) below
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself, either Perl version 5.8.9 or, at
your option, any later version of Perl 5 you may have available.
This library is distributed in the hope that it will be useful, but
without any warranty; without even the implied warranty of
merchantability or fitness for a particular purpose.
SEE ALSO
autobox
Moose::Autobox
Perl6::Contexts
<
http://github.com/gitpan/autobox-Core>
IO::Any
Perl 6: <
http://dev.perl.org/perl6/apocalypse/>.
(Shameless plug:) *Perl 6 Now: The Core Ideas Illustrated with Perl 5*
dedicates a sizable portion of Chapter 14, Objects, to autoboxing and
the idea is used heavily throughout the book. Chapter 8, Data
Structures, also has numerous examples. See <
http://perl6now.com> or
look for ISBN 1-59059-395-2 at your favorite bookstore for more
information.
AUTHORS
Scott Walters,
[email protected].
Michael Schwern and the perl5i contributors for tests, code, and
feedback.
JJ contributed a "strip" method for scalars - thanks JJ!
Ricardo SIGNES contributed patches.
Thanks to Matt Spear, who contributed tests and definitions for numeric
operations.
Mitchell N Charity reported a bug and sent a fix.
Thanks to chocolateboy for autobox and for the encouragement.
Thanks to Bruno Vecchi for bug fixes and many, many new tests going into
version 0.8.
Thanks to <
http://github.com/daxim> daxim/Lars DIECKOW pushing in fixes
and patches from the RT queue along with fixes to build and additional
doc examples.
