[slf4j-dev] Release of SLF4J version 1.6.0-RC0

[Ceki Gülcü]

I believe(d) that adding methods to an interface impacts client code
using interface beyond the actual implementations of the
interface. This is not true in simple cases, for example when the
implementations change in accordance with changes in the
interface. Obviously, when client code uses a newly added method in an
interface and the interface available on the class path is older,
one is sure to run into problems.  I wonder if there are other
problematic cases.

If my assumption about new methods impacting client code is wrong,
then that opens new possibilities.

On 24/04/2010 3:55 PM, Joern Huxhorn wrote:
> Hi Ceki,
>
> On 24.04.2010, at 13:44, Ceki Gülcü <ceki at qos.ch> wrote:
>
>>
>> Hi Joern,
>>
>> On 24/04/2010 1:55 AM, Joern Huxhorn wrote:
>>> Hi Ceki,
>>>
>>> On 23.04.2010, at 16:18, Ceki Gülcü <ceki at qos.ch> wrote:
>>>
>>>> On 23/04/2010 2:14 PM, Joern Huxhorn wrote:
>>>>> Didn't you change LocationAwareLogger and doesn't that mean that it's
>>>>> not compatible with the current Logback anymore?
>>>>> Or is this only relevant for wrappers like jcl-over-slf4j and you
>>>>> changed all of them already?
>>>>
>>>>
>>>> Right, LocationAwareLogger affects compatibility with logback but so
>>>> does MessageFormatter changes, actually the latter in a deeper way as
>>>> it is no longer possible to compute the formatted message lazily in
>>>> LoggingEvent. I must be computed eagerly in LoggingEvent's constructor.
>>>>
>>>
>>> Are you aware that my ParameterizedMessage supports both #70 and lazy
>>> initialization?
>>
>> Yes, but ParameterizedMessage has to be passed as a Message to a
>> logger of type org.slf4j.n.Logger. More below.
>>
>>> This is possible since the placeholders are only counted during
>>> creation. The actual formatting/placeholder replacement is only
>>> performed when the formatted message is requested. The formatted message
>>> is kept so it won't be regenerated in case of further calls.
>>> It could also be enhanced to perform the toString of the arguments at a
>>> later time. The Message interface could be extended by an
>>> prepareForDeferredProcessing() method for that purpose.
>>>
>>> I agree with Ralph that this would be a good time to extend the Logger
>>> interface with Message-aware methods since 1.6 will be incompatible
>>> anyway.
>>
>> Initially, I also thought that 1.6.0 was a good time to integrate your
>> changes.
>>
>> Changing the Logger interface breaks compatibility with client code
>> using SLF4J. Breaking compatibility at this level is different than
>> breaking compatibility within SLF4J internals. For example, as long as
>> the end-user places slf4j-api-1.6.0.jar and an appropriate 1.6.0
>> binding on the class path, things will work fine without needing to
>> compile client code or dependencies. However, if the logger interface
>> was changed, then *all* client code (including all dependencies using
>> SLF4J) would need to be recompiled. There is no comparison in the
>> impact of changing SLF4J internals and changing client-facing
>> interfaces such as org.slf4j.Logger.
>>
>
> Yes, I understand.
> That's why I'd suggest to add Message-aware methods, leaving the
> existing ones untouched.
>
> One of my goals in slf4j-n was to reduce the number of methods in the
> Logger interface.
> This was seemingly a bad idea since it would have a performance impact,
> in the case where a message isn't actually logged, as Ralph reported.
>
> Because of this, it would be very wise to keep all the methods that are
> already present in the Logger interface and simply add
> debug(Message)
> debug(Message, Throwable)
> debug(Marker, Message)
> debug(Marker, Message, Throwable)
> [same for other levels plus generic log(Level, ...)-methods]
>
> The designer in me doesn't like the "bloated" (in the sense that some
> methods could be dropped without losing functionality) interface, but
> the realist in me accepts that performance is more important than
> aesthetics ;)
>
> The big advantage, on the other hand, would be that the interfaces would
> indeed stay compile-time compatible.
>
> I only dropped this requirement since I assumed that the original
> slf4j-api was absolutely frozen (and I still think that it would be a
> good idea to keep it that way...).
>
> slf4j-api and slf4j-n-api were meant to exist side by side, with the
> former ensuring backwards-compatibility with Java 1.4 and slf4j-n-api
> for explicit opt-in to new functionality by changing the imports of
> Logger and LoggerFactory.
>
> If the preconditions of a frozen slf4j-api and Java 1.4 compatibility
> have been dropped, there's no use for a separate slf4j-n-api and we can
> simply extend the current Logger interface with the previously mentioned
> methods.
>
> Cheers,
> Joern.
> _______________________________________________
> slf4j-dev mailing list
> slf4j-dev at qos.ch
> http://qos.ch/mailman/listinfo/slf4j-dev