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Manpages fieldsSection: Perl Programmers Reference Guide (3perl)Updated: 2001-02-22 Index Return to Main Contents NAMEfields - compile-time class fieldsSYNOPSIS{ package Foo; use fields qw(foo bar _Foo_private); sub new { my Foo $self = shift; unless (ref $self) { $self = fields::new($self); $self->{_Foo_private} = "this is Foo's secret"; } $self->{foo} = 10; $self->{bar} = 20; return $self; } } my Foo $var = Foo::->new; $var->{foo} = 42; # this will generate a compile-time error $var->{zap} = 42; # subclassing { package Bar; use base 'Foo'; use fields qw(baz _Bar_private); # not shared with Foo sub new { my $class = shift; my $self = fields::new($class); $self->SUPER::new(); # init base fields $self->{baz} = 10; # init own fields $self->{_Bar_private} = "this is Bar's secret"; return $self; } } DESCRIPTIONThe "fields" pragma enables compile-time verified class fields.NOTE: The current implementation keeps the declared fields in the %FIELDS hash of the calling package, but this may change in future versions. Do not update the %FIELDS hash directly, because it must be created at compile-time for it to be fully useful, as is done by this pragma. If a typed lexical variable holding a reference is used to access a hash element and a package with the same name as the type has declared class fields using this pragma, then the operation is turned into an array access at compile time. The related "base" pragma will combine fields from base classes and any fields declared using the "fields" pragma. This enables field inheritance to work properly. Field names that start with an underscore character are made private to the class and are not visible to subclasses. Inherited fields can be overridden but will generate a warning if used together with the "-w" switch. The effect of all this is that you can have objects with named fields which are as compact and as fast arrays to access. This only works as long as the objects are accessed through properly typed variables. If the objects are not typed, access is only checked at run time. The following functions are supported:
SEE ALSObase, ``Pseudo-hashes: Using an array as a hash'' in perlref
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