that's "terminology injection" (aka die "brain overflow" ;-)
Ha ha, I noticed a mind-boggling number of different ways to do this type of stuff in Perl.
For example,
chromatic refers
here
to a modernperlbooks article which gives the illustrative example below:
At its core, dependency injection is a formalization of the design principle "Don't hard-code your dependencies." Consider the code:
sub fetch
{
my ($self, $uri) = @_;
my $ua = LWP::UserAgent->new;
my $resp = $ua->get( $uri );
...
}
That's not bad code by any means, but it's a little too specific and a little less generic due to the presence of the literal string LWP::UserAgent.
That might be fine for your application, but that hard-coding introduces a coupling that can work against other uses of this code. Imagine testing this code, for example.
While you could use Test::MockObject to intercept calls to LWP::UserAgent's constructor, that approach manipulates Perl symbol tables to work around a hard coded dependency.
An alternate approach uses a touch of indirection to allow for greater genericity:
use Moose;
has 'ua', is => 'ro', default => sub { LWP::UserAgent->new };
sub fetch
{
my ($self, $uri) = @_;
my $ua = $self->ua;
my $resp = $ua->get( $uri );
...
}
Now the choice of user agent is up to the code which constructs this object.
If it provides a ua to the constructor, fetch() will use that. Otherwise, the default behavior is to use LWP::UserAgent as before.
Lots of stuff on CPAN too:
As usual, the hard part is knowing which is good and which is crap.
Please let us know of other cool CPAN offerings I've overlooked.
