NAME
Sub::Trigger::Lock - a coderef for use in Moose triggers that will lock
hashrefs and arrayrefs
SYNOPSIS
This module provides the antidote for:
package Foo {
use Moose;
has bar => (is => 'ro', isa => 'ArrayRef');
}
my $foo = Foo->new( bar => [1,2,3] );
push @{ $foo->bar }, 4; # does not die!
All you need to do is:
package Foo {
use Moose;
use Sub::Trigger::Lock;
has bar => (is => 'ro', isa => 'ArrayRef', trigger => Lock);
}
Or, a shortcut:
package Foo {
use Moose;
use Sub::Trigger::Lock qw(RO);
has bar => (is => RO, isa => 'ArrayRef');
}
TL;DR
Force modifications of your arrayref/hashref attributes to be made via
your documented API.
DESCRIPTION
This module provides two constants, `Lock` and `RO`. The first of these is
the only one exported by default, and the key to understanding this
module. This module also provides the utility functions `lock` and
`unlock`, which are not exported by default.
`Lock`
`Lock` is a constant which evaluates to a coderef. The coderef takes
two or more arguments. That is, `Lock` itself takes no arguments; it
returns a coderef that takes arguments!
The first argument is supposed to be a blessed object, but it is
actually completely ignored.
If the second argument is not a hashref or arrayref, it is also
ignored. Everything is ignored! But if the second argument *is* a
hashref or arrayref, it will be flagged as read-only.
This is a fairly shallow read-only flag. Attempts to add or remove
keys from the hash, or change the value for any key will throw an
exception. But if the value is reference to some other structure, that
structure will be unaffected.
Similarly, attempts to push, pop, shift, or unshift a read-only array,
or to change the value for any index will throw an exception. Buf if
the values are references to other structures, these will also be
unaffected.
Overall, the effect of `Lock` is that you can do something like this:
package Person {
use Moose;
has name => (is => 'ro', writer => 'set_name');
}
package Band {
use Moose;
use Sub::Trigger::Lock;
has members => (is => 'ro', trigger => Lock);
}
my $spice_girls = Band->new(
members => [
Person->new(name => 'Victoria Adams'),
Person->new(name => 'Melanie Brown'),
Person->new(name => 'Emma Bunton'),
Person->new(name => 'Melanie Chisholm'),
Person->new(name => 'Geri Halliwell'),
],
);
# This is OK, because deep changes work
$spice_girls->members->[0]->set_name('Victoria Beckham');
# This is not OK, because shallow changes throw!
$spice_girls->members->[0] = Person->new(name => 'Johnny Cash');
`RO`
`RO` is a constant that evaluates to the list:
'ro', 'trigger', Lock,
`lock($ref)`
A utility function for locking an arrayref or hashref in the same way
that the `Lock` coderef would.
`unlock($ref)`
A utility function for unlocking an arrayref or hashref.
Note that this returns a *guard object*. You should store this object
in a variable. Once the object is destroyed (e.g. because the variable
has gone out of scope), $ref will be automatically locked again!
This allows you to temporarily unlock a hashref or arrayref in order
to privately manipulate it:
package Band {
use Moose;
use Sub::Trigger::Lock qw( Lock unlock );
has members => (is => 'ro', trigger => Lock);
sub add_members {
my ($self, @members) = @_;
my $guard = unlock( $self->members );
push @{$self->members}, @members;
}
}
IMPLEMENTATION NOTES
This module uses the Perl internal `Internals::SvREADONLY` function for
most of the heavy lifting. This is much, much faster than ties.
BUGS
Please report any bugs to
<
http://rt.cpan.org/Dist/Display.html?Queue=Sub-Trigger-Lock>.
SEE ALSO
Exporter::Tiny, Scope::Guard.
AUTHOR
Toby Inkster <
[email protected]>.
COPYRIGHT AND LICENCE
This software is copyright (c) 2014 by Toby Inkster.
This is free software; you can redistribute it and/or modify it under the
same terms as the Perl 5 programming language system itself.
DISCLAIMER OF WARRANTIES
THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
