Scalar::Properties(3) User Contributed Perl DocumentationScalar::Properties(3)NAMEScalar::Properties - run-time properties on scalar variables
SYNOPSIS
use Scalar::Properties;
my $val = 0->true;
if ($val && $val == 0) {
print "yup, its true alright...\n";
}
my @text = (
'hello world'->greeting(1),
'forget it',
'hi there'->greeting(1),
);
print grep { $_->is_greeting } @text;
my $l = 'hello world'->length;
DESCRIPTIONScalar::Properties attempts to make Perl more object-oriented by taking
an idea from Ruby: Everything you manipulate is an object, and the
results of those manipulations are objects themselves.
'hello world'->length
(-1234)->abs
"oh my god, it's full of properties"->index('g')
The first example asks a string to calculate its length. The second
example asks a number to calculate its absolute value. And the third
example asks a string to find the index of the letter 'g'.
Using this module you can have run-time properties on initialized
scalar variables and literal values. The word 'properties' is used in
the Perl 6 sense: out-of-band data, little sticky notes that are
attached to the value. While attributes (as in Perl 5's attribute
pragma, and see the "Attribute::*" family of modules) are handled at
compile-time, properties are handled at run-time.
Internally properties are implemented by making their values into
objects with overloaded operators. The actual properties are then
simply hash entries.
Most properties are simply notes you attach to the value, but some may
have deeper meaning. For example, the "true" and "false" properties
plays a role in boolean context, as the first example of the Synopsis
shows.
Properties can also be propagated between values. For details, see the
EXPORTS section below. Here is an example why this might be desirable:
pass_on('approximate');
my $pi = 3->approximate(1);
my $circ = 2 * $rad * $pi;
# now $circ->approximate indicates that this value was derived
# from approximate values
Please don't use properties whose name start with an underscore; these
are reserved for internal use.
You can set and query properties like this:
"$var->myprop(1)"
sets the property to a true value.
"$var->myprop(0)"
sets the property to a false value. Note that this doesn't delete
the property (to do so, use the "del_props" method described
below).
"$var->is_myprop", "$var->has_myprop"
returns a true value if the property is set (i.e., defined and has
a true value). The two alternate interfaces are provided to make
querying attributes sound more natural. For example:
$foo->is_approximate;
$bar->has_history;
METHODS
Values thus made into objects also expose various utility methods. All
of those methods (unless noted otherwise) return the result as an
overloaded value ready to take properties and method calls itself, and
don't modify the original value.
INTROSPECTIVE METHODS
These methods help in managing a value's properties.
"$var-"get_props>
Get a list of names of the value's properties.
"$var-"del_props(LIST)>
Deletes one or more properties from the value. This is different
than setting the property value to zero.
"$var-"del_all_props>
Deletes all of the value's properties.
NUMERICAL METHODS
"plus(EXPR)"
Returns the value that is the sum of the value whose method has
been called and the argument value. This method also overloads
addition, so:
$a = 7 + 2;
$a = 7->plus(2); # the same
"minus(EXPR)"
Returns the value that is the the value whose method has been
called minus the argument value. This method also overloads
subtraction.
"times(EXPR)"
Returns the value that is the the value whose method has been
called times the argument value. This method also overloads
multiplication.
"divide(EXPR)"
Returns the value that is the the value whose method has been
called divided by the argument value. This method also overloads
division.
"modulo(EXPR)"
Returns the value that is the the value whose method has been
called modulo the argument value. This method also overloads the
modulo operator.
"exp(EXPR)"
Returns the value that is the the value whose method has been
called powered by the argument value. This method also overloads
the exponentiation operator.
"abs"
Returns the absolute of the value.
"zero"
Returns a boolean value indicating whether the value is equal to 0.
STRING METHODS
"length", "size"
Returns the result of the built-in "length" function applied to the
value.
"reverse"
Returns the reverse string of the value.
"uc", "ucfirst", "lc", "lcfirst", "hex", "oct"
Return the result of the appropriate built-in function applied to
the value.
"concat(EXPR)", "append(EXPR)"
Returns the result of the argument expression appended to the
value.
"swapcase"
Returns a version of the value with every character's case
reversed, i.e. a lowercase character becomes uppercase and vice
versa.
"split /PATTERN/, LIMIT"
Returns a list of overloaded values that is the result of splitting
(according to the built-in "split" function) the value along the
pattern, into a number of values up to the limit.
BOOLEAN METHODS
"numcmp(EXPR)"
Returns the (overloaded) value of the numerical three-way
comparison. This method also overloads the "<=>" operator.
"cmp(EXPR)"
Returns the (overloaded) value of the alphabetical three-way
comparison. This method also overloads the "cmp" operator.
"eq(EXPR)", "ne(EXPR)", "lt(EXPR)", "gt(EXPR)", "le(EXPR)", "ge(EXPR)"
Return the (overlaoded) boolean value of the appropriate string
comparison. These methods also overload those operators.
"eqi(EXPR)", "nei(EXPR)", "lti(EXPR)", "gti(EXPR)", "lei(EXPR)",
"gei(EXPR)"
These methods are case-insensitive versions of the above operators.
"is_true", "is_false"
Returns the (overloaded) boolean status of the value.
EXPORTS
Three subroutines dealing with how properties are propagated are
automatically exported. For an example of propagation, see the
DESCRIPTION section above.
"pass_on(LIST)"
Sets (replaces) the list of properties that are passed on. There is
only one such list for the whole mechanism. The whole property
interface is experimental, but this one in particular is likely to
change in the future.
"passed_on(STRING)"
Tests whether a property is passed on and returns a boolean value.
"get_pass_on"
Returns a list of names of properties that are passed on.
TAGS
If you talk about this module in blogs, on del.icio.us or anywhere
else, please use the "scalarproperties" tag.
BUGS AND LIMITATIONS
No bugs have been reported.
Please report any bugs or feature requests to
"bug-scalar-properties@rt.cpan.org", or through the web interface at
<http://rt.cpan.org>.
INSTALLATION
See perlmodinstall for information and options on installing Perl
modules.
AVAILABILITY
The latest version of this module is available from the Comprehensive
Perl Archive Network (CPAN). Visit <http://www.perl.com/CPAN/> to find
a CPAN site near you. Or see
<http://www.perl.com/CPAN/authors/id/M/MA/MARCEL/>.
AUTHORS
Marcel Gruenauer, "<marcel@cpan.org>"
James A. Duncan "<jduncan@fotango.com>"
Some contributions from David Cantrell, "<david@cantrell.org.uk>"
COPYRIGHT AND LICENSE
Copyright 2001-2007 by Marcel Gruenauer
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
perl v5.14.1 2007-10-18 Scalar::Properties(3)
