ideas.pod

Stuff to Cover

Encapsulation

Private / Friend / Family / Public

Don't Double Check

Let's imagine my "Org" class takes a database handle as an attribute. It doesn't actually perform any queries on the database, but needs to pass it on to any "Dept" objects it instantiates.

Then Org should not perform a type check on the database handle. Org should rely on Dept to check its own parameters. Org should just pass on whatever value it receives.

Double checking needlessly slows down instantiating Org objects, and makes Org less flexible. If a future version (or a subclass) of Dept accepts, say, a path to a CSV file as an alternative to a database handle, then Org's insistance on only accepting database handles starts to look silly.

Immutable objects

http://blogs.perl.org/users/mascip/2014/06/immutability-with-moose.html

Enumerations

http://blogs.perl.org/users/toby_inkster/2014/05/enumerations-in-moose.html

Exceptions

http://www.perlmonks.org/index.pl?node_id=1092576

Coderefs

Coderefs have various uses in Perl, but for object-oriented programming, there are two patterns which stand out:

Coderefs are single-use objects

A coderef $o is a classless object with a single (unnamed) method:

$o->method(@args)     # normal object
$o->(@args)           # coderef "object"

Note that overloading allows blessed objects to support the unnamed method call too.

One particular case of this pattern is where the coderef acts as a factory - i.e. an object thats sole purpose is to instantiate other objects.

Coderefs are mobile methods

A coderef $method is a method that is independent of classes and roles, and can thus be called on any object, bypassing method resolution:

$o->method(@args)     # normal method call
$o->$method(@args)    # coderef "method"

Doing this with overloading is tricky because Perl stringifies blessed methods instead of codulating them.

Callbacks should be implemented this way, with the first parameter as an invocant:

my $app = MyApp->new;
$app->register_foo_callback(sub {
   my $app = shift;  # don't just close over $app because ref cycles
});