When thinking of agile software development and all the principles (SRP, OCP, ...) I ask myself how to treat logging.
Is logging next to an implementation a SRP violation?
I would say
yes because the implementation should be also able to run without logging. So how can I implement logging in a better way? I've checked some patterns and came to a conclusion that the best way not to violate the principles in a user-defined way, but to use any pattern which is known to violate a principle is to use a decorator pattern.
Let's say we have a bunch of components completely without SRP violation and then we want to add logging.
- component A
- component B uses A
We want logging for A, so we create another component D decorated with A both implementing an interface I.
- interface I
- component L (logging component of the system)
- component A implements I
- component D implements I, decorates/uses A, uses L for logging
- component B uses an I
Advantages: - I can use A without logging - testing A means I don't need any logging mocks - tests are simpler
Disadvantage: - more components and more tests
I know this seem to be another open discussion question, but I actually want to know if someone uses better logging strategies than a decorator or SRP violation. What about static singleton logger which are as default NullLogger and if syslog-logging is wanted, one change the implementation object at runtime?