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On 03/12/2012 08:58 PM, Adam Young wrote:
>
>>
>>     Also, these global objects force us to do a bunch of hacks in unit
>>     tests. We need to do tricks to ensure the object is initialized as
>>     we want. We also need to save and restore its state between runs.
>>
>>
>> I don't agree with the statement that they force "a bunch of hacks,"
>> clearing
>> state is a perfectly normal thing to do, it is done for any servers
>> that get
>> started, any mocks that are made, and every test database. Making sure
>> that
>> modifications to a configuration object are cleaned up is no
>> different: there
>> is no "save and restore" just always start from a blank slate and set
>> things
>> as required, same as in the non-global model.
>>
> But ensuring that we are back at tabular rasa is difficult with global
> objects and running tests in a single process space. Many of the test
> cases are dependant on second order effects of function calls to
> configure internal objects, instead of being true unit tests that only
> call on a single object.
>
> This kind of refactoring is the norm in large projects, and leads to
> better tested code paths, reusuable objects, and objects that are easier
> to understand and track.
>
> One way that these types of things have been described is via the SOLID
> acronym. THis is a collection of best practices:
>
> http://en.wikipedia.org/wiki/SOLID_%28object-oriented_design%29
>
> The Global config violates quite a few of these principals. By reading
> from a configuration object, you implicitly violate Single
> responsibility. Now it has at least two, one of which is figuring out
> how to construct and initialize itself. It also doesn't really follow
> the Open Closed principal: Once you get state from a Config object, you
> can no longer easily extend it, unless that extended object also gets
> its state from the same config. The big one is D: Dependency. By using a
> global config, you make dependencies on implementations, not
> abstractions. Dependency injection is pretty much impossible with a
> global config.

++

-jay