Hi guys,
On 24.04.2010, at 18:00, Ralph Goers <[email protected]> wrote:
Adding new methods to an interface only affects implementations of
that interface, not clients of the interface. So backward
compatibility is maintained.
Yes, this is the case.
Clients compiled against the original interface will work using the
extended one.
This is exactly why I chose to implement the Message support the way
I did. Complete backward compatibility is maintained. I believe
Joern's implementation is a little different and has a bigger impact
as it provides a how new api layer instead of extending the existing
interface.
Indeed.
I developed it with the assumption that the Logger interface must not
be extended under any circumstance.
IIRC Joern didn't go so far as to modify all the logback internals
where the Logback in my fork does.
Yes, I didn't touch Logback at all.
slf4j-n-api was meant as a base of further discussion. Your findings
concerning performance invalidated my reduction of the interface, though
I have one remaining headache:
I'd really, really like to have generic methods that log with a Level
parameter.
This would be an ideal place for an enum but we are still staying 1.4
for now, right?
If we are not using an enum now, we won't be able to switch to an enum
at a later time without breaking binary compatibility.
Because of that, I'd suggest to keep those generic log methods out of
the interface until we actually switch to 1.5 altogether - even though
I have several places where I could use that functionality very well!
Cheers & have a nice weekend,
Joern.
Ralph
On Apr 24, 2010, at 7:50 AM, Ceki Gülcü wrote:
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 <[email protected]> wrote:
Hi Joern,
On 24/04/2010 1:55 AM, Joern Huxhorn wrote:
Hi Ceki,
On 23.04.2010, at 16:18, Ceki Gülcü <[email protected]> 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.
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