On 3/22/10 4:42 PM, Lukas Kahwe Smith wrote:
On 22.03.2010, at 16:35, Nils Adermann wrote:
I agree that type hinting actual implementations, read classes, is a
bad
idea. But I fail to see why having an interface definition for each
service is a bad idea. Even without type hinting every service
implementation will have to follow an implicit interface convention
anyway, otherwise you wouldn't be able to replace the service with a
different one at all. So if you develop a new service you will need to
implement this implicit interface, so why not make it explicit?
You mention having to extend classes to be able to add the service
interface. I assume you are talking about classes that already exist
which you want to make available as services. Now with those classes,
isn't it pure luck if they already implement the implicit interface -
meaning they already have the right method signatures? Typically you
would either have to extend them or add proxies to delegate calls to
make sure the right method signatures are exposed. Such subclass or
proxies could again explicitly implement the interface easily.
You are of course right. I also thought about this and came to the conclusion
that it really depends on the service. Like many caching layers have pretty
much exactly the same API. In some cases you might be only using a limited set
of methods. But that also means that your dependency is a bit fragile I guess.
So yes I can totally see myself making frequent use of interfaces to be able to
type hint, but I am not sure if we should make this a must use feature in order
to get the injection to work. Not even sure if it should be natively supported
as an option.
The Symfony Dependency Injection does not rely on type hinting for
injection. You can use it for other purposes, but it is not used by
Symfony directly.
Fabien
But just to make my response clear: Yes in most cases you will probably need to stick
some wrapper/proxy in front of the third party anyways and then you might as well also
add the "implements [service name]" and having an interface around for each
interface is also a nice piece of documentation for people wondering what they need to
implement to be able to replace a service and for people who want to check on what they
can rely on that is provided by the service. Documentation through code is always a good
thing.
regards,
Lukas Kahwe Smith
[email protected]
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