package Class::Trait;
use strict;
use warnings;
our $VERSION = '0.31';
use overload ();
use File::Spec ();
use B qw/svref_2object/;
use Scalar::Util qw/blessed/;
sub _croak($) {
my $message = shift;
require Carp;
Carp::croak($message);
}
sub _sub_package {
my $package;
eval {
my $stash = svref_2object(shift)->STASH;
if ( $stash && $stash->can('NAME') ) {
$package = $stash->NAME;
}
else {
$package = '';
}
};
if ($@) {
warn "Could not determine calling package: $@";
}
return $package;
}
## ----------------------------------------------------------------------------
## Debugging functions
## ----------------------------------------------------------------------------
# make a sub
sub DEBUG {0}
require Data::Dumper if DEBUG;
# this is accessable to the package
my $debug_indent = 0;
{
# this however is not accessable to anyone but the debug function
my $debug_line_number = 1;
# debuggin'
sub debug {
return unless DEBUG;
# otherwise debug
my $formatted_debug_line_number
= sprintf( "%03d", $debug_line_number );
print STDERR "debug=($formatted_debug_line_number) ",
( " " x $debug_indent ), @_, "\n";
$debug_line_number++;
}
}
## ----------------------------------------------------------------------------
# This allows us to rename "does" to something which does not conflict with a
# method in the current package. Also, for backwards compatability, one can
# specifiy Class::Trait->relation('is');
my $NAME_FOR_DOES = 'does';
sub _name_for_does {
$NAME_FOR_DOES;
}
# XXX OK, admit it. This function is a right mess. I'm embarrassed.
my %PACKAGE_DOES;
my $DOES = sub {
my $proto = shift;
my $class = ref($proto) || $proto;
my $trait;
if ( !$proto->isa('Class::Trait::Config') ) {
no strict 'refs';
$trait = ${"${class}::TRAITS"} or do {
# if we've gotten to here, then the TRAITS are not defined in the
# current package. This implies that we have a subclass
# inheriting from a class which uses traits and the does() method
# needs to search the inheritance heirarchy.
foreach my $parent ( @{"${class}::ISA"} ) {
my @result = $parent->$NAME_FOR_DOES(@_)
if $parent->can($NAME_FOR_DOES);
next unless @result;
if (@_) {
return $result[0] || ();
}
return @result;
}
};
}
else {
$trait = $proto;
}
if (@_) {
my $trait_name = shift;
if ( exists $PACKAGE_DOES{$class}{$trait_name} ) {
return 1;
}
my $does = _recursive_does( $trait, $trait_name );
return $does if $does;
# we have runtime traits applied to instances
if ( $class =~ /__ANON__/ ) {
no strict 'refs';
($class)
= @{"${class}::ISA"}; # ANON traits have single inheritance
return $class->$NAME_FOR_DOES($trait_name)
if $class->can($NAME_FOR_DOES);
}
return $does;
}
else {
my %does = map { $_ => 1 } _all_does($trait),
keys %{ $PACKAGE_DOES{$class} };
# we have runtime traits applied to instances
if ( $class =~ /__ANON__/ ) {
no strict 'refs';
($class)
= @{"${class}::ISA"}; # ANON traits have single inheritance
if ( $class->can($NAME_FOR_DOES) ) {
foreach my $does ( $class->$NAME_FOR_DOES ) {
$does{$does} = 1;
}
}
if ( exists $PACKAGE_DOES{$class} ) {
foreach my $does ( keys %{ $PACKAGE_DOES{$class} } ) {
$does{$does} = 1;
}
}
}
return keys %does;
}
};
# a trait cache, so we can avoid re-processing traits we already have
# processed. This is checked by the trait_load function prior to reading the
# trait in
my %CACHE = ();
# load the config class
use Class::Trait::Config;
# base class for traits
use Class::Trait::Base;
# save packages that need to be checked for meeting requirements here
my %TRAITS_TO_CHECK = ();
sub _clear_all_caches {
%CACHE = ();
%TRAITS_TO_CHECK = ();
}
# XXX this is merely a testing hook
sub _clear_does_cache {
%PACKAGE_DOES = ();
}
# these traits are supplied "for free"
my $TRAIT_LIB_ROOT = File::Spec->catfile(qw(Class Trait Lib));
my %TRAIT_LIB = map { $_ => 1 }
qw(
TEquality
TPrintable
TComparable
);
## ----------------------------------------------------------------------------
sub import {
my $class = shift;
# just loading the module does not mean we have any traits to give it, so
# we return if there is nothing
return unless @_;
# but if we have something, then ...
my ($package) = caller();
# if we are being asked to make a trait a trait then ...
if ( $_[0] eq "debug" ) {
no strict 'refs';
no warnings 'redefine';
*{"Class::Trait::DEBUG"} = sub {1};
}
elsif ( $_[0] eq "base" ) {
no strict 'refs';
# push our base into the front
# of the ISA list
unshift @{"${package}::ISA"} => 'Class::Trait::Base';
if ( defined( my $name_for_does = $_[1] ) ) {
$class->_set_does( $package, $name_for_does );
}
}
# otherwise we are using traits
else {
if (DEBUG) {
debug "^ compiling/processing traits for $package";
$debug_indent++;
}
_apply_traits( $package, _compile_traits( $package, @_ ) );
$debug_indent-- if DEBUG;
}
}
# XXX we kick the anonymous counter every time we apply a trait to an instance
# in order to guarantee that no two anonymous classes can ever share the same
# name.
my $anon_counter = 1;
sub apply {
my ( $class, $proto, @traits ) = @_;
# failing to clear the caches means that trait information from one
# instance can bleed to another when resolving conflicts
_clear_all_caches();
my $target_class =
blessed $proto
? _setup_anonymous_class( $proto, @traits )
: $proto;
eval {
_apply_traits(
$target_class, _compile_traits( $target_class, @traits ),
1
);
};
_croak $@ if $@;
if ( blessed $proto) {
# XXX bless the object after attempting to apply traits. Otherwise,
# someone at the top level could be applying a trait in an eval and
# getting the object blessed into the new class even though the trait
# application failed.
bless $proto, $target_class;
}
$class->initialize;
return $class;
}
sub _setup_anonymous_class {
my ( $instance, @traits ) = @_;
my $name = join( '', grep { !ref } @traits ) . "_" . $anon_counter++;
my $package = ref $instance;
if ( $package =~ /^(.*)?::__ANON__::/ ) {
$package = $1; # trim old anonymous info
}
my $anon_class = "${package}::__ANON__::$name";
{
no strict 'refs';
@{"${anon_class}::ISA"} = ref $instance;
}
return $anon_class;
}
sub _apply_traits {
my ( $package, $composite_trait_config, $override_methods ) = @_;
if (DEBUG) {
debug "> proccessing traits for $package";
$debug_indent++;
}
if ( $package->isa('Class::Trait::Base') ) {
_apply_traits_to_trait( $package, $composite_trait_config );
}
else {
# we now apply the traits in the BEGIN phase this allows the modules
# to be used under mod_perl, however see the documentation for some
# important caveats
_apply_traits_to_package(
$package, $composite_trait_config,
$override_methods
);
# we still do try to verify the traits in the INIT phase
debug "~ verification of traits for $package scheduled for INIT phase"
if DEBUG;
$TRAITS_TO_CHECK{$package} = $composite_trait_config;
}
if (DEBUG) {
$debug_indent--;
debug "< finished proccessing traits for $package";
}
}
NOWARN: {
no warnings 'void'; # XXX keep mod_perl happy
# INIT now just runs initialize
INIT {
initialize() if keys %TRAITS_TO_CHECK;
}
}
# initialize checks that all the traits requirements have been fufilled
sub initialize {
if (DEBUG) {
debug "> verifiying traits in packages";
$debug_indent++;
}
my ( $package, $trait );
while ( ( $package, $trait ) = each %TRAITS_TO_CHECK ) {
_check_traits_in_package( $package, $trait );
}
if (DEBUG) {
$debug_indent--;
debug "> finished verifiying traits in packages";
}
}
sub _check_traits_in_package {
my ( $package, $trait ) = @_;
if (DEBUG) {
debug "? verifying $package has no conflicts with $trait->{name}";
$debug_indent++;
}
my @conflicting_methods;
while ( my ( $method, $conflict ) = each %{ $trait->conflicts } ) {
if ($conflict) {
push @conflicting_methods, $method;
}
}
if (@conflicting_methods) {
@conflicting_methods = sort @conflicting_methods;
_croak
"Package $package has conflicting methods (@conflicting_methods)";
}
$debug_indent-- if DEBUG;
if (DEBUG) {
debug
"? verifying $package fufills the requirements for $trait->{name}";
$debug_indent++;
}
foreach my $requirement ( keys %{ $trait->requirements } ) {
# if the requirement is an operator then we need to put the paren in
# front, as that is how overload.pm does it, this will tell us if the
# operator has been overloaded or not
$requirement = "($requirement" unless is_method_label($requirement);
# now check if the package fufills the requirement or not, and croak if
# it fails
unless ( $package->can($requirement) ) {
_croak
"Requirement ($requirement) for $trait->{name} not in $package";
}
# if it doesn't fail we can go on to the next
debug
"+ requirement ($requirement) for $trait->{name} fufilled in $package"
if DEBUG;
}
$debug_indent-- if DEBUG;
}
## ----------------------------------------------------------------------------
## trait-to-package application
## ----------------------------------------------------------------------------
sub _apply_traits_to_package {
my ( $package, $trait, $override_methods ) = @_;
if (DEBUG) {
debug "@ applying trait ($trait->{name}) to package ($package)";
$debug_indent++;
}
_add_trait_methods( $package, $trait, $override_methods );
_add_trait_overloads( $package, $trait, $override_methods );
if (DEBUG) {
$debug_indent--;
debug "^ storing reference to traits in $package";
}
# now storing the trait in the package so that it can be accessable
# through reflection.
no strict 'refs';
*{"${package}::TRAITS"} = \$trait;
__PACKAGE__->_set_does($package);
}
sub rename_does {
shift; # Class::Trait;
my ($package) = caller();
__PACKAGE__->_set_does( $package, @_ );
}
sub _set_does {
my ( $class, $package ) = splice @_, 0, 2;
if (@_) {
my $name_for_does = shift;
if ( !is_method_label($name_for_does) ) {
_croak "Illegal name for trait relation method ($name_for_does)";
}
$NAME_FOR_DOES = $name_for_does;
}
no strict 'refs';
no warnings 'redefine';
*{"${package}::$NAME_FOR_DOES"} = $DOES;
return $package;
}
sub _all_does {
my $trait = shift;
my %trait_does;
foreach my $sub_trait ( @{ $trait->sub_traits } ) {
$trait_does{$sub_trait} = 1;
foreach my $sub_sub_trait ( _all_does( $CACHE{$sub_trait} ) ) {
$trait_does{$sub_sub_trait} = 1;
}
}
return keys %trait_does;
}
sub _recursive_does {
my ( $trait, $trait_name ) = @_;
return 1 if ( $trait->name eq $trait_name );
foreach my $sub_trait_name ( @{ $trait->sub_traits } ) {
# if its on the second level, then we are here
return 1 if ( $sub_trait_name eq $trait_name );
# if not, then we need to descend lower
return 1
if ( _recursive_does( $CACHE{$sub_trait_name}, $trait_name ) );
}
return 0;
}
# -----------------------------------------------
# private methods used by trait application
# -----------------------------------------------
sub _add_trait_methods {
my ( $package, $trait, $override_methods ) = @_;
if (DEBUG) {
debug "> adding trait ($trait->{name}) methods into $package";
$debug_indent++;
}
my ( $method_label, $method );
while ( ( $method_label, $method ) = each %{ $trait->methods } ) {
# NOTE: we allow this routine to check our package for an implemented
# method since it is possible that some other package implemented it
# before traits did. It is however unlikely. We know too that all
# methods will be installed, and that the local implementations will
# overwrite these.
no strict 'refs';
if ( !defined &{"${package}::$method_label"} || $override_methods ) {
# we add it ....
debug "+ adding method ($method_label) into $package" if DEBUG;
# suppress redefined warnings because traits applied to classes at
# runtime are treated as "mixins"
no warnings 'redefine';
eval qq{
package $package;
sub $method_label { $method(\@_) }
};
}
else {
# otherwise we let the local class's version override the trait version
debug "~ $package locally implements method ($method_label)"
if DEBUG;
}
}
$debug_indent-- if DEBUG;
}
sub _add_trait_overloads {
my ( $package, $trait, $override_operators ) = @_;
if (DEBUG) {
debug "> adding trait ($trait->{name}) overloads into $package";
$debug_indent++;
}
# make sure we don't overwrite any overloads so we must first check to see
# if they are defined in the local class and build a temporary set of
# overloads to apply.
my %overloads = ( fallback => 1 );
my ( $operator, $method_label );
while ( ( $operator, $method_label ) = each %{ $trait->overloads } ) {
# NOTE: we allow this routine to check our package for an implemented
# operator since it is possible that "overload" was called before the
# trait is
if ( !defined &{"${package}::($operator"} || $override_operators ) {
debug "+ adding operator ($operator) into $package" if DEBUG;
$overloads{$operator} = $method_label;
}
else {
debug "~ $package locally implements operator ($operator)"
if DEBUG;
}
}
$debug_indent-- if DEBUG;
# now add the temporary set of overloads we build
overload::OVERLOAD( $package, %overloads );
}
## ----------------------------------------------------------------------------
## trait-to-trait application
## ----------------------------------------------------------------------------
sub _apply_traits_to_trait {
my ( $package, $trait ) = @_;
debug "^ storing sub-traits ($trait->{name}) into trait $package"
if DEBUG;
no strict 'refs';
*{"${package}::TRAITS"} = $trait;
}
## ----------------------------------------------------------------------------
## trait compiling
## ----------------------------------------------------------------------------
# takes a trait declaration and compiles it into a trait configuration we can
# use to apply to a particular package
# NOTE: this function utilizes functions from the section labled "trait
# operations", which can be found at line no. 505
sub _compile_traits {
my ( $package, @trait_declarations ) = @_;
if (DEBUG) {
debug "> compiling traits for $package";
$debug_indent++;
}
# now we can process our traits
my @traits = ();
# loop through the declarations
while ( defined( my $trait_name = shift @trait_declarations ) ) {
$PACKAGE_DOES{$package}{$trait_name} = 1;
# get the name
if (DEBUG) {
debug "+ found trait ($trait_name)";
$debug_indent++;
}
# and load the trait
my $trait_config = _load_trait($trait_name);
# then if the next element is a hash ref meaning there are changes to
# be made to the trait (exclusion or aliasing), then process that
# accordingly
if ( ref( $trait_declarations[0] ) eq "HASH" ) {
if (DEBUG) {
debug
"+ found trait declarations for $trait_name in $package";
$debug_indent++;
}
# get the changes
my $trait_changes = shift @trait_declarations;
# check for aliases first
# NOTE: we need to do this before we check for excludes to allow
# for a method to be aliased to a new name, then the old name
# excluded to avoid a conflict.
if ( exists ${$trait_changes}{alias} ) {
if (DEBUG) {
debug "> found alias declaration";
$debug_indent++;
}
_alias_trait_methods(
$trait_config,
%{ $trait_changes->{alias} }
);
$debug_indent-- if DEBUG;
}
# now check for exludes
if ( defined( my $excludes = ${$trait_changes}{exclude} ) ) {
if (DEBUG) {
debug "> found exclude declaration";
$debug_indent++;
}
$excludes = [$excludes] unless 'ARRAY' eq ref $excludes;
_exclude_trait_methods( $trait_config, $excludes );
$debug_indent-- if DEBUG;
}
$debug_indent-- if DEBUG;
debug
"< finished processing trait declarations for $trait_name in $package"
if DEBUG;
}
# our trait is all ready now, so we can then push it onto the list
push @traits => $trait_config;
$debug_indent-- if DEBUG;
}
# finally sum them all together into one config (minus any overriding
# trait)
my $composite_trait_config = _sum_traits(@traits);
if (DEBUG) {
$debug_indent--;
debug "< finished compling traits for $package";
}
# now our composite trait is complete
return $composite_trait_config;
}
## ----------------------------------------------------------------------------
## trait loader
## ----------------------------------------------------------------------------
sub _load_trait {
my ($trait) = @_;
# check first to see if we already
# have the trait in our cache
if ( exists $CACHE{$trait} ) {
debug "~ found trait ($trait) in cache" if DEBUG;
# return a copy out of our cache
return __PACKAGE__->fetch_trait_from_cache($trait);
}
if (DEBUG) {
debug "> loading trait ($trait)";
$debug_indent++;
debug "+ requiring ${trait}.pm";
$debug_indent++;
}
# load the trait ...
if ( exists $TRAIT_LIB{$trait} ) {
debug "! ${trait} is in our trait lib, ... loading from lib" if DEBUG;
eval {
require File::Spec->catfile( $TRAIT_LIB_ROOT, "${trait}.pm" );
};
}
else {
eval "require ${trait}";
}
$debug_indent-- if DEBUG;
if ($@) {
_croak "Trait ($trait) could not be found : $@";
}
# otherwise ...
# check to make sure it is the proper type
$trait->isa('Class::Trait::Base')
|| _croak
"$trait is not a proper trait (inherits from Class::Trait::Base)";
# initialize our trait configuration
my $trait_config = Class::Trait::Config->new();
$trait_config->name($trait);
_get_trait_requirements($trait_config);
_get_trait_methods($trait_config);
_get_trait_overloads($trait_config);
no strict 'refs';
# if this trait has sub-traits, we need to process them.
no warnings 'once';
if ( $trait->isa('Class::Trait::Base') && keys %{"${trait}::TRAITS"} )
{
if (DEBUG) {
debug "! found sub-traits in trait ($trait)";
$debug_indent++;
}
$trait_config
= _override_trait( \%{"${trait}::TRAITS"}, $trait_config );
if (DEBUG) {
$debug_indent--;
debug "< dumping trait ($trait) with subtraits ("
. ( join ", " => @{ $trait_config->sub_traits } ) . ") : "
. Data::Dumper::Dumper($trait_config);
}
}
# put the trait into the cache to avoid having to be processed again
_store_trait_in_cache( $trait, $trait_config );
{
# traits should be able to tell us which other traits they do
no strict 'refs';
no warnings 'redefine';
*{"Class::Trait::Config::$NAME_FOR_DOES"} = $DOES;
}
if (DEBUG) {
$debug_indent--;
debug "< finished loading trait ($trait)";
}
# then return the fresh config
return $trait_config;
}
# -----------------------------------------------
# private methods used by trait loader
# -----------------------------------------------
sub _override_trait {
my ( $trait, $overriding_trait ) = @_;
# create a new trait config to represent the combined traits
my $trait_config = Class::Trait::Config->new();
$trait_config->name($overriding_trait->name);
$trait_config->sub_traits([
# if we have a composite trait we dont want to include the name here
# as it is actually defined better in the sub_traits field, but if we
# don't have a composite, then we want to include the trait name
( ( COMPOSITE() eq $trait->name ) ? () : $trait->name ),
@{ $trait->sub_traits }
]);
# let the overriding trait override the methods in the regular trait
$trait_config->methods(
{ %{ $trait->methods }, %{ $overriding_trait->methods } }
);
# the same for overloads
$trait_config->overloads(
{ %{ $trait->overloads }, %{ $overriding_trait->overloads } }
);
# now combine the requirements as well
$trait_config->requirements(
{ %{ $trait->requirements }, %{ $overriding_trait->requirements } }
);
if (DEBUG) {
debug "? checking for requirement fufillment";
$debug_indent++;
}
# but we need to check them
foreach my $requirement ( keys %{ $trait_config->requirements } ) {
if ( is_method_label($requirement) ) {
if ( exists ${ $trait_config->methods }{$requirement} ) {
debug
"+ method requirement ($requirement) is fufilled in overriding trait"
if DEBUG;
delete ${ $trait_config->requirements }{$requirement};
next;
}
}
else {
if ( exists ${ $trait_config->overloads }{$requirement} ) {
debug
"+ overload requirement ($requirement) is fufilled in overriding trait"
if DEBUG;
delete ${ $trait_config->requirements }{$requirement};
next;
}
}
debug "* requirement ($requirement) not fufilled in overriding trait"
if DEBUG;
}
if (DEBUG) {
$debug_indent--;
debug "? checking for conflict resultion";
$debug_indent++;
}
# now deal with conflicts
foreach my $conflict ( keys %{ $trait->conflicts } ) {
if ( is_method_label($conflict) ) {
if ( exists ${ $trait_config->methods }{$conflict} ) {
debug
"+ method conflict ($conflict) is resolved in overriding trait"
if DEBUG;
delete ${ $trait_config->requirements }{$conflict};
next;
}
}
else {
if ( exists ${ $trait_config->overloads }{$conflict} ) {
debug
"+ overload conflict ($conflict) is resolved in overriding trait"
if DEBUG;
delete ${ $trait_config->requirements }{$conflict};
next;
}
}
debug "* conflict ($conflict) not resolved in overriding trait"
if DEBUG;
$trait_config->conflicts->{$conflict}++;
}
$debug_indent-- if DEBUG;
return $trait_config;
}
sub _get_trait_requirements {
my ($trait_config) = @_;
# this function messes with symbol tables and symbol refs, so turn strict
# off in its context
no strict 'refs';
( defined $trait_config->name )
|| _croak
"Trait must be loaded first before information can be gathered";
my $trait = $trait_config->name;
debug "< getting requirements for ${trait}" if DEBUG;
# get any requirements in the trait and turn it into a hash so we can
# track stuff easier
$trait_config->requirements({ map { $_ => 1 } @{"${trait}::REQUIRES"} })
if defined @{"${trait}::"}{REQUIRES};
}
sub _get_trait_methods {
my ($trait_config) = @_;
( defined $trait_config->name )
|| _croak
"Trait must be loaded first before information can be gathered";
my $trait = $trait_config->name;
debug "< getting methods for ${trait}" if DEBUG;
# this function messes with symbol tables and symbol refs, so turn strict
# off in its context
no strict 'refs';
my %implementation_for;
foreach ( keys %{"${trait}::"} ) {
my $method = "${trait}::$_";
next unless defined &$method;
# make sure we're not grabbing sub imported into the trait
next unless _sub_package( \&$method ) eq $trait;
if (/(DESTROY|AUTOLOAD)/) {
_croak "Trait $trait attempted to implement disallowed method $1";
}
$implementation_for{$_} = $method;
}
$trait_config->methods(\%implementation_for);
}
sub _get_trait_overloads {
my ($trait_config) = @_;
# this function messes with symbol tables and symbol refs, so turn strict
# off in its context
no strict 'refs';
( defined $trait_config->name )
|| _croak
"Trait must be loaded first before information can be gathered";
my $trait = $trait_config->name;
debug "< getting overloads for ${trait}" if DEBUG;
# get the overload parameter hash
no warnings 'once';
$trait_config->overloads({ %{"${trait}::OVERLOADS"} })
if keys %{"${trait}::OVERLOADS"};
}
## ----------------------------------------------------------------------------
## trait cache operations
## ----------------------------------------------------------------------------
# NOTE: the traits are stored as a copy and then fetched as a copy. This is
# because we alter our version when we apply declarations (excludes, aliases),
# and so we need to make sure our cache stays clean.
sub _store_trait_in_cache {
my ( $trait_name, $trait_config ) = @_;
debug "^ storing ($trait_name) in cache" if DEBUG;
$CACHE{$trait_name} = $trait_config->clone();
}
sub fetch_trait_from_cache {
my ( $class, $trait_name ) = @_;
debug "< fetching ($trait_name) from cache" if DEBUG;
return $CACHE{$trait_name}->clone();
}
## ----------------------------------------------------------------------------
## trait operations
## ----------------------------------------------------------------------------
# -----------------------------------------------
# exclusion
# -----------------------------------------------
sub _exclude_trait_methods {
my ( $trait_config, $exclusions ) = @_;
if (DEBUG) {
debug "- excluding methods for trait ($trait_config->{name})";
$debug_indent++;
}
foreach my $exclusion (@$exclusions) {
# check we have the method being excluded
( exists ${ $trait_config->methods }{$exclusion} )
# otherwise we throw an exception here
|| _croak
"Attempt to exclude method ($exclusion) that is not in trait ($trait_config->{name})";
debug "- excluding method ($exclusion)" if DEBUG;
# if we do have it, so lets exclude it
delete ${ $trait_config->methods }{$exclusion};
# and be sure to add it to the list of requirements
# unless its already there
$trait_config->requirements->{$exclusion}++;
}
$debug_indent-- if DEBUG;
}
# -----------------------------------------------
# aliasing
# -----------------------------------------------
sub _alias_trait_methods {
my ( $trait_config, %aliases ) = @_;
debug "=> aliasing methods for trait ($trait_config->{name})" if DEBUG;
# Now when aliasing methods for a trait, we need to be sure to move any
# operator overloads that are bound to the old method to use the new
# method this helps us assure that the intentions of trait is fufilled. So
# to facilitate this, we reverse the normal overload hash (operator =>
# method) to be keyed by method (method => operator), this way we can
# access it easier.
my %overloads_by_method = reverse %{ $trait_config->overloads };
# no process the aliases
$debug_indent++ if DEBUG;
foreach my $old_name ( keys %aliases ) {
# check we have the method being aliases
exists ${ $trait_config->methods }{$old_name}
# otherwise we throw an exception here
|| _croak
"Attempt to alias method ($old_name) that is not in trait ($trait_config->{name})";
debug "=> aliasing method ($old_name) to ($aliases{$old_name})"
if DEBUG;
# if we do have it, so lets alias it
$trait_config->methods->{ $aliases{$old_name} }
= $trait_config->methods->{$old_name};
# if we find the old method in the overloads,
# then we change it to the new one here
$trait_config->overloads->{ $overloads_by_method{$old_name} }
= $aliases{new_name}
if exists $overloads_by_method{$old_name};
}
$debug_indent-- if DEBUG;
}
# -----------------------------------------------
# summation
# -----------------------------------------------
# a constant to represent the name of a composite trait, a composite trait's
# name is best described as the concatenation of all the names of its
# subtraits, but rather than duplicate that information in the name field and
# the sub-traits field, we assign a COMPOSITE constant as a placeholder/flag
use constant COMPOSITE => "COMPOSITE";
sub _sum_traits {
my (@traits) = @_;
if ( scalar @traits == 1 ) {
# if we have only one trait, it doesn't make sense to sum it since
# there is nothing to sum it against
debug "< only one trait, no need to sum" if DEBUG;
return $traits[0];
}
debug "> summing traits ("
. ( join ", " => map { $_->{name} } @traits ) . ")"
if DEBUG;
# initialize our trait configuration
my $trait_config = Class::Trait::Config->new();
# we are making a composite trait, so lets call it as such
$trait_config->name(COMPOSITE);
$debug_indent++ if DEBUG;
# and process our traits
foreach my $trait (@traits) {
push @{ $trait_config->sub_traits } => $trait->name;
if (DEBUG) {
debug "+ adding trait ($trait->{name}) to composite trait";
$debug_indent++;
}
# first lets check the methods
_fold_in_methods( $trait, $trait_config );
# then check the overloads
_fold_in_overloads( $trait, $trait_config );
$debug_indent-- if DEBUG;
}
$debug_indent-- if DEBUG;
# now that we have added all our methods we can check to see if any of our
# requirements have been fufilled during that time
if (DEBUG) {
debug
"? checking requirements for sum-ed traits ($trait_config->{name})";
$debug_indent++;
}
foreach my $trait (@traits) {
_check_requirements( $trait, $trait_config );
}
$debug_indent-- if DEBUG;
# now we have cleared up any requirements and combined all our methods, we
# can return the config
debug "< traits summed successfully" if DEBUG;
return $trait_config;
}
# -----------------------------------------------
# private methods used by summation
# -----------------------------------------------
sub _fold_in_methods {
my ( $trait, $trait_config ) = @_;
if (DEBUG) {
debug "> folding in methods for trait ($trait->{name})";
$debug_indent++;
}
foreach my $method_label ( keys %{ $trait->methods } ) {
if ( exists ${ $trait_config->conflicts }{$method_label} ) {
debug "* method ($method_label) is already in conflict" if DEBUG;
# move to the next method as we cannot add this one
next;
}
# if the method label already exists in our combined config, then ...
if ( exists ${ $trait_config->methods }{$method_label} ) {
# check to make sure it is not the same method possibly from a
# shared base/sub-trait
unless ( $trait_config->methods->{$method_label} eq
$trait->methods->{$method_label} )
{
# this is a conflict, we need to add the method label onto the
# requirements and we need to label that a method is in
# conflict.
debug
"* method ($method_label) is in conflict, added to the requirements"
if DEBUG;
# method is in conflict...
$trait_config->conflicts->{$method_label}++;
# so remove any copies ...
delete ${ $trait_config->methods }{$method_label};
# and it is considered to be a requirement
# for the implementing class
$trait_config->requirements->{$method_label}++;
}
else {
debug
"~ method ($method_label) is a duplicate, no action was taken"
if DEBUG;
}
}
else {
debug "+ method ($method_label) added successfully" if DEBUG;
# move it
$trait_config->methods->{$method_label}
= $trait->methods->{$method_label};
}
}
$debug_indent-- if DEBUG;
}
sub _fold_in_overloads {
my ( $trait, $trait_config ) = @_;
if (DEBUG) {
debug "> folding in overloads for trait ($trait->{name})";
$debug_indent++;
}
foreach my $overload ( keys %{ $trait->overloads } ) {
if ( exists ${ $trait_config->conflicts }{$overload} ) {
debug "* overload ($overload) is already in conflict" if DEBUG;
# move to the next overload as we cannot add this one
next;
}
# if we already have it then
if ( exists ${ $trait_config->overloads }{$overload} ) {
# before we get hasty, lets check out if the method called for
# this overload is also in conflict (which if it isn't likely
# means that they were the same method) (see method equality
# function)
my $overload_method = ${ $trait_config->overloads }{$overload};
unless ( ${ $trait_config->conflicts }{$overload_method} ) {
debug
"~ operator ($overload) is a duplicate, no action was taken"
if DEBUG;
next;
}
debug "* operator ($overload) in conflict, added to requirements"
if DEBUG;
# note the conflict and ...
$trait_config->conflicts->{$overload}++;
# get rid of it (conflicts results in exclusions)
delete ${ $trait_config->overloads }{$overload};
# since the overload is now excluded, then it then
# becomes a requirement for the implementing package
$trait_config->requirements->{"${overload}"}++;
}
else {
debug "+ operator ($overload) added successfully" if DEBUG;
# otherwise add it to the list of methods
$trait_config->overloads->{$overload}
= $trait->overloads->{$overload};
}
}
$debug_indent-- if DEBUG;
}
sub _check_requirements {
my ( $trait, $trait_config ) = @_;
# now check the requirements
debug "? checking for trait ($trait->{name})" if DEBUG;
foreach my $requirement ( keys %{ $trait->requirements } ) {
# if the method does not exist in
# our new combined method group
unless ( exists ${ $trait_config->methods }{$requirement} ) {
if (DEBUG) {
$debug_indent++;
debug "* requirement ($requirement) not fufilled";
$debug_indent--;
}
# make it a reuiqement for the package
$trait_config->requirements->{$requirement}++;
}
}
}
## ----------------------------------------------------------------------------
## utility methods
## ----------------------------------------------------------------------------
# short quick predicate functions
sub is_method_label { $_[0] =~ /[[:alpha:]][[:word:]]+/ }
1;
__END__
=head1 NAME
Class::Trait - Deprecated. Please use Moose::Role.
=head1 SYNOPSIS
# to turn on debugging (do this before
# any other traits are loaded)
use Class::Trait 'debug';
# nothing happens, but the module is loaded
use Class::Trait;
# loads these two traits and flatten them
# into the current package
use Class::Trait qw(TPrintable TComparable);
# loading a trait and performing some
# trait operations (alias, exclude) first
use Class::Trait (
'TPrintable' => {
alias => { "stringValue" => "strVal" },
exclude => "stringValue",
},
);
# loading two traits and performing
# a trait operation (exclude) on one
# module to avoid method conflicts
use Class::Trait
'TComparable' => {
# exclude the basic equality method
# from TComparable and use the ones
# in TEquality instead.
exclude => [ "notEqualTo", "equalTo" ]
},
'TEquality' # <- use equalTo and notEqualTo from here
);
# when building a trait, you need it
# to inherit from the trait meta/base-class
# so do this ...
use Class::Trait 'base';
=head1 DESCRIPTION
This document attempts to explain Traits in terms of Perl.
=head2 Trait composition
A Trait can be defined as a package containing:
=over 4
=item *
A set of methods
=item *
A hash of overloaded operators mapped to the method labels
=item *
An array of required method labels
=back
Here is an example of the syntax for a very basic trait:
package TPrintable;
use Class::Trait 'base';
our @REQUIRES = qw(toString);
our %OVERLOADS = ('""' => toString);
sub stringValue {
my ($self) = @_;
require overload;
return overload::StrVal($self);
}
1;
The above example requires the user of the trait to implement a C<toString>
method, which the overloaded C<""> operator then utilizes. The trait also
provides a C<stringValue> method to the consuming class.
=head2 Trait usage
When a class uses a Trait:
=over 4
=item * Requirements
All requirements of the traits (or composite trait) must be meet either by the
class itself or by one of its base classes.
=item * Flattening
All the non-conflicting trait (or composite trait) methods are flattened into
the class, meaning an entry is created directly in the class's symbol table
and aliased to the original trait method. Only methods defined in the trait
are used. Subroutines imported into the trait are not used.
=item * Conflicts
If a method label in a class conflicts with a method label in the trait (or
composite trait), the class method is chosen and the trait method is
discarded. This only applies to methods defined directly in the class's symbol
table, methods inherited from a base class are overridden by the trait method.
=back
Here is a simple example of the usage of the above trait in a class.
package MyClass;
use Class::Trait (
'TPrintable' => {
alias => { "strVal" => "stringValue" }
exclude => "stringValue",
}
);
sub stringValue { ... }
The above example would use the C<TPrintable> trait, aliasing C<stringValue>
to the method label C<strVal>, and then excluding C<stringValue>. This is done
to avoid a conflict with C<stringValue> method implemented in the class that
uses the trait.
=head2 Trait operations
When using a trait, the class can make changes to the structure of a trait
through the following methods.
=over 4
=item * Exclusion
An array of method labels to exclude from trait. If only a single method
needs to be excluded, you may provide the method name without an array.
=item * Alias
A hash of old method labels to new method labels.
=item * Summation
A number of traits can be combined into one.
=back
=head3 Exclusion
This excludes a method from inclusion in the class which is using the trait.
It does however cause the method to be added to the traits required methods.
This is done because it is possible that other methods within the trait rely
on the excluded method, and therefore it must be implemented somewhere in
order for the other method to work.
=head3 Aliasing
Aliasing is not renaming or redefining, it does not remove the old method, but
instead just introduces another label for that method. The old method label
can be overridden or excluded without affecting the new method label.
One special note is that aliasing does move any entry in the overloaded
operators to use the new method name, rather than the old method name. This is
done since many times aliasing is used in conjunction with exclusion to
pre-resolve conflicts. This avoids the orphaning of the operator.
=head3 Summation
When two or more traits are used by a class (or another trait), the traits are
first compiled into a composite trait. The resulting composite trait is:
=over 4
=item * Methods
A union of all non-conflicting methods of all traits.
=item * Operators
A union of all non-conflicting operators of all traits.
=item * Requirements
A union of all unsatisfied requirements of all traits.
=back
=head4 Method conflicts
Method equality if determined by two conditions, the first being method label
string equality, the second being the hex address of the code reference (found
by stringifying the subroutine reference).
If a method in one of the traits is deemed to be in conflict with a method in
another trait, the result is the exclusion of that method from the composite
trait. The method label is then added to the requirements array for the
composite trait.
Method conflict can be avoided by using exclusion or a combination of aliasing
and exclusion.
=head4 Operator conflicts
Operator conflicts also result in the exclusion of the operator from the
composite trait and the operator then becomes a requirement.
=head4 Requirement satisfaction
One trait may satisfy the requirements of another trait when they are combined
into a composite trait. This results in the removal of the requirement from
the requirements array in the composite trait.
=head1 RUNTIME TRAIT APPLICATION
As of C<Class::Trait> version 0.20, you can now apply traits at runtime to
both classes and instances by using the C<apply()> method. Applying a trait
at runtime is similar to using the trait as a mixin because existing methods
will be overwritten.
The syntax is:
Class::Trait->apply($class_or_instance, @list_of_traits);
=head2 Classes
Applying a trait at runtime to a class:
if ($secure) {
Class::Trait->apply($class_name, 'TSecureConnection');
}
else {
warn "Using insecure connections";
Class::Trait->apply($class_name, 'TInsecureConnection');
}
Now all instances of C<$class_name> will have the methods provided by the
trait applied. If the trait applied at runtime provides methods already
defined in C<$class_name>, the C<$class_name> methods will be silently
redefined with the trait's methods.
=head2 Instances
Applying a trait at runtime to an instance:
if ($secure) {
Class::Trait->apply($instance, 'TSecureConnection');
}
else {
warn "Using insecure connections";
Class::Trait->apply($instance, 'TInsecureConnection');
}
When applying a trait (or set of traits) to an instance of a class, B<only>
that instance gets the new methods. If you want numerous instances to receive
the new methods, either apply the trait to all instances or consider applying
it to the class.
Note that the instance is blessed into a new, anonymous class and it's this
class which contains the new methods.
=head1 WHEN TO USE TRAITS
For a relatively simple class heirarchy you may need traits. There are,
however, several key indicators that traits may be beneficial for you.
=over 4
=item * Duplicated behavior
Whenever you've duplicated behavior across unrelated classes.
=item * Multiple inheritance
Any time you might think about MI and it's only for code reuse (in other
words, the subclass is not a more specific type of a super class)
=item * Interfaces
Any time you might want a Java-style interface but you also want an
implementation to go with that.
=item * Mixins
Any time you might want to use mixins (have you ever considered exporting
methods?)
=back
=head1 EXPORTS
=over 4
=item * B<$TRAITS>
While not really exported, Class::Trait leaves the actual Class::Trait::Config
object applied to the package stored as scalar in the package variable at
C<$TRAITS>.
=item * B<does>
Class::Trait will export this method into any object which uses traits. By
calling this method you can query the kind of traits the object has
implemented. The method works much like the perl C<isa> method in that it
performs a depth-first search of the traits hierarchy and returns true (1) if
the object implements the trait, and false (0) otherwise.
$my_object_with_traits->does('TPrintable');
Calling C<does> without arguments will return all traits an ojbect does.
=item * B<is>
Class::Trait used to export this method to any object which uses traits, but
it was found to conflict with Test::More::is. The recommended way is to use
C<does>.
To use C<is> instead of C<does>, one trait must use the following syntax for
inheritance:
use Class::Trait qw/base is/;
Instead of:
use Class::Trait 'base';
It is recommended that all traits use this syntax if necessary as the
mysterious "action at a distance" of renaming this method can be confusing.
As an alternative, you can also simply use the following in any code which
uses traits:
BEGIN {
require Class::Trait;
Class::Trait->rename_does('is');
}
This is generally not recommended in test suites as Test::More::is() conflicts
with this method.
=back
=head1 METHODS
=over 4
=item B<initialize>
Class::Trait uses the INIT phase of the perl compiler, which will not run
under mod_perl or if a package is loaded at runtime with C<require>. In order
to insure that all traits a properly verified, this method must be called.
However, you may still use Class::Trait without doing this, for more details
see the L<CAVEAT> section.
=item B<rename_does>
Note: You probably do not want to use this method.
Class::Trait uses C<does()> to determine if a class can "do" a particular
trait. However, your package may already have a C<does()> method defined or
you may be migrating from an older version of L<Class::Trait> which uses
C<is()> to perform this function. To rename C<does()> to something more
suitable, you can use this at the top of your code:
BEGIN {
require Class::Trait; # we do not want to call import()
Class::Trait->rename_does($some_other_method_name);
}
use Class::Trait 'some_trait';
If you wish to shield your users from seeing this, you can declare any trait
with:
use Class::Trait qw/base performs/; # 'performs' can be any valid method name
You only need to do that in one trait and all traits will pick up the new
method name.
=back
=head1 TRAIT LIBRARY
I have moved some of the traits in the test suite to be used outside of this,
and put them in what I am calling the trait library. This trait library will
hopefully become a rich set of base level traits to use when composing your
own traits. Currently there are the following pre-defined traits.
=over 4
=item * TPrintable
=item * TEquality
=item * TComparable
=back
These can be loaded as normal traits would be loaded, Class::Trait will know
where to find them. For more information about them, see their own
documenation.
=head1 DEBUGGING
Class::Trait is really an experimental module. It is not ready yet to be used
seriously in production systems. That said, about half of the code in this
module is dedicated to formatting and printing out debug statements to STDERR
when the debug flag is turned on.
use Class::Trait 'debug';
The debug statements prints out pretty much every action taken during the
traits compilation process and on occasion dump out B<Data::Dumper> output of
trait structures. If you are at all interested in traits or in this module, I
recommend doing this, it will give you lots of insight as to what is going on
behind the scences.
=head1 CAVEAT
This module uses the INIT phase of the perl compiler to do a final check of
the of the traits. Mostly it checkes that the traits requirements are fufilled
and that your class is safe to use. This presents a problem in two specific
cases.
=over 5
=item B<Under mod_perl>
mod_perl loads B<all> code through some form of eval. It does this I<after>
the normal compilation phases are complete. This means we cannot run INIT.
=item B<Runtime loading>
If you load code with C<require> or C<eval "use Module"> the result is the
same as with mod_perl. It is post-compilation, and the INIT phase cannot be
run.
=back
However, this does not mean you cannot use Class::Trait in these two
scenarios. Class::Trait will just not check its requirements, these routines
will simply throw an error if called.
The best way to avoid this is to call the class method C<initialize>, after
you have loaded all your classes which utilize traits, or after you
specifically load a class with traits at runtime.
Class::Trait->initialize();
This will result in the final checking over of your classes and traits, and
throw an exception if there is a problem.
Some people may not object to this not-so-strict behavior, the smalltalk
implementation of traits, written by the authors of the original papers
behaves in a similar way. Here is a quote from a discussion I had with
Nathanael Scharli, about the Smalltalk versions behavior:
Well, in Squeak (as in the other Smalltalk dialects), the difference
between runtime and compile time is not as clear as in most other
programming languages. The reason for this is that programming in
Smalltalk is very interactive and there is no explicit compile phase.
This means that whenever a Smalltalk programmer adds or modifies a method,
it gets immediately (and automatically) compiled and installed in the
class. (Since Smalltalk is not statically typed, there are no type checks
performed at compile time, and this is why compiling a method simply means
creating and installing the byte-code of that method).
However, I actually like if the programmer gets as much static information
bout the code as possible. Therefore, my implementation automaticelly
checks the open requirements whenever a method gets
added/removed/modified. This means that in my implementation, the
programmer gets interactive feedback about which requirements are still to
be satisfied while he is composing the traits together. In particular, I
also indicate when all the requirements of a class/trait are fulfilled. In
case of classes, this means for the programmer that it is now possible to
actually use the class without running into open requirements.
However, according to the Smalltalk tradition, I do not prevent a
programmer from instantiating a class that still has open requirements.
(This can be useful if a programmer wants to test a certain functionality
of a class before it is actually complete). Of course, there is then
always the risk that there will be a runtime error because of an
unsatisfied requirement.
As a summary, I would say that my implementation of traits keeps track of
the requirements at compile time. However, if an incomplete class (i.e., a
class with open requirements) is instantiated, unfulfilled requirements
result in a runtime error when they are called.
=head1 TO DO
I consider this implementation of Traits to be pretty much feature complete in
terms of the description found in the papers. Of course improvements can
always be made, below is a list of items on my to do list:
=over 4
=item B<Tests>
I have revamped the test suite alot this time around. But it could always use
more. Currently we have 158 tests in the suite. I ran it through Devel::Cover
and found that the coverage is pretty good, but can use some help:
---------------------------- ------ ------ ------ ------ ------ ------ ------
File stmt branch cond sub pod time total
---------------------------- ------ ------ ------ ------ ------ ------ ------
/Class/Trait.pm 91.4 58.6 50.0 95.7 6.2 8.9 80.0
/Class/Trait/Base.pm 90.5 50.0 n/a 100.0 n/a 0.1 83.9
/Class/Trait/Config.pm 100.0 n/a n/a 100.0 100.0 2.9 100.0
---------------------------- ------ ------ ------ ------ ------ ------ ------
Obviously Class::Trait::Config is fine.
To start with Class::Trait::Reflection is not even tested at all. I am not
totally happy with this API yet, so I am avoiding doing this for now.
The pod coverage is really low in Class::Trait since virtually none of the
methods are documented (as they are not public and have no need to be
documented). The branch coverage is low too because of all the debug
statements that are not getting execute (since we do not have DEBUG on).
The branch coverage in Class::Trait::Base is somwhat difficult. Those are
mostly rare error conditions and edge cases, none the less I would still like
to test them.
Mostly what remains that I would like to test is the error cases. I need to
test that Class::Traits blows up in the places I expect it to.
=item B<Improve mod_perl/INIT phase solution>
Currently the work around for the mod_perl/INIT phase issue (see L<CAVEAT>) is
to just let the unfufilled requirement routines fail normally with perl. Maybe
I am a control freak, but I would like to be able to make these unfufilled
methods throw my own exceptions instead. My solution was to make a bunch of
stub routines for all the requirements. The problem is that I get a bunch of
"subroutine redeined" warnings coming up when the local method definitions are
installed by perl normally.
Also, since we are installing our methods and our overloads into the class in
the BEGIN phase now, it is possible that we will get subroutine redefinition
errors if there is a local implementation of a method or operator. This is
somewhat rare, so I am not as concerned about that now.
Ideally I would like to find a way around the INIT issue, which will still
have the elegance of using INIT.
=item B<Reflection API>
The class Class::Traits::Reflection gives a basic API to access to the traits
used by a class. Improvements can be made to this API as well as the
information it supplies.
=item B<Tools>
Being a relatively new concept, Traits can be difficult to digest and
understand. The original papers does a pretty good job, but even they stress
the usefulness of tools to help in the development and understanding of
Traits. The 'debug' setting of Class::Trait gives a glut of information on
every step of the process, but is only useful to a point. A Traits 'browser'
is something I have been toying with, both as a command line tool and a Tk
based tool.
=item B<Trait Lib>
In this release I have added some pre-built traits that can be used;
TEquality, TComparable, TPrintable. I want to make more of these, it will only
help.
=back
=head1 PRIVATE METHODS IN TRAITS
Sometimes a trait will want to define private methods that only it can see.
Any subroutine imported into the trait from outside of the trait will
automatically be excluded. However, a trait can define private methods by
using anonymous subroutines.
package TSomeTrait;
use Class::Trait 'base';
my $private = sub { ... };
sub public {
my $self = shift;
my $data = $self->$private;
...
}
=head1 ACKNOWLEDGEMENTS
=over 4
=item * Curtis "Ovid" Poe
Initial idea and code for this module.
=item * Nathanael Scharli and the Traits research group.
Answering some of my questions.
=item * Yuval Kogman
Spotting the problem with loading traits with :: in them. Thanks to Curtis
"Ovid" Poe for bringing it up again, and prompting me to release the fix.
=item * Roman Daniel
Fixing SUPER:: handling.
=item * Curtis "Ovid" Poe
The code to change C<is> to C<does>.
=back
=head1 SEE ALSO
Class::Trait is an implementation of Traits as described in the the documents
found on this site L<http://www.iam.unibe.ch/~scg/Research/Traits/>. In
particular the paper "Traits - A Formal Model", as well as another paper on
statically-typed traits (which is found here :
L<http://www.cs.uchicago.edu/research/publications/techreports/TR-2003-13>).
=head1 ERROR MESSAGES
=head2 Redefined subroutine warnings
If a class using a trait has a method which the trait defines, the class's
method is assumed to be the correct method. However, you should get a
"Subroutine redefined" warning. To avoid this, explicitly exclude the method:
use Class::Trait TSomeTrait => { exclude => 'foo' };
sub foo {}
Sometimes you will see strange warnings such as:
Subroutine Circle::(== redefined at /usr/lib/perl5/5.8.7/overload.pm at ...
This is because traits can support overloading. To avoid this warning, define
your overloaded methods prior to using L<Class::Trait>.
use overload ( '==' => \&equalTo );
use Class::Trait
"TCircle" => { exclude => 'equalTo' },
"TColor" => { exclude => 'equalTo' };
=head1 BUGS
=head2 does
When applying traits at runtime to instances, the following works:
$object->does($some_trait_name);
However, normally we should be able to do the following and get a list of all
traits the instance does:
my @does = $object->does;
Currently, this returns no traits. It will be fixed in a future release.
=head1 MAINTAINER
Curtis "Ovid" Poe, C<< <ovid [at] cpan [dot] org> >>
=head1 AUTHOR
stevan little, E<lt>stevan@iinteractive.comE<gt>
The development of this module was initially begun by Curtis "Ovid" Poe,
E<lt>poec@yahoo.comE<gt>.
=head1 COPYRIGHT AND LICENSE
Copyright 2004, 2005 by Infinity Interactive, Inc.
L<http://www.iinteractive.com>
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.
=cut