Re: [equinox-dev] boolean properties etc

[David M Williams <david_williams@xxxxxxxxxx>]

Makes sense to me. 

Another possible advantage of enumerated
attribute values is that there might be some cases where 'systemDefault'
would be a good option, 
so that some "meta data" could
specify "use form=jar/dir unless otherwise specified". 
I don't know if that particular example
is valid, or how many cases this would be needed or make sense ... so,
take with a grain of salt. 
But, I've actually seen this anti-pattern?
a lot with "user preferences" ... the intial tendancy is often
to think of some user preference as "on or off" but 50% of the
time 
the next release reveals more cases
... "not specified by user" being an obvious third choice. 

But, for manifests, couldn't "true/false"
usually be deprecated, and future versions be spec'd as multivalued (and
'true', 'false' be assigned to one of the new states, for backward
compatibility?). But I do agree, its
just more meaningful to spec what you mean :)

Jeff McAffer <Jeff_McAffer@xxxxxxxxxx>
Sent by: equinox-dev-bounces@xxxxxxxxxxx

09/28/2006 11:11 PM

Please respond to
Equinox development mailing list <equinox-dev@xxxxxxxxxxx>

To	equinox-dev@xxxxxxxxxxx
cc
Subject	[equinox-dev] boolean properties etc

There have been several cases lately where we are being burned by having
used boolean values for properties, headers, ...  In particular, things
like 
        unpack=true/false 
        Eclipse-LazyStart: true/false
are problematic for a few reasons.   

- First we seem to have this tendency to specify them in the negative.
 For example unpack=false is the default way we want things.  That
approach made sense in the context of the day but today it is just hard
to deal with the double negative.   

- It is not always clear what the property is controlling.  unpack,
for example, is somewhat cryptic. 

- Perhaps the most interesting issue relates to extensibility.  Eclipse-LazyStart:
true/false has only two possible values.  Recently there has been
some discussion about adding an eager mode.  Ignoring the details
of that request and assuming we did want this, with only true and false
for Lazy start, we would have to add another header for eager mode.

An alternative would be to avoid headers, arguments, properties etc that
have boolean values.  Instead of unpack = true/false, use something
like form=jar/dir.  Eclipse-LazyStart would be something like Eclipse-BundleStart:
lazy/manual/eager.  This approach is more extensible and seems easier
to usnderstand. Note also that these headers can have additional information
provided as attributes or directives in the standard OSGi manner.

Thoughts 
Jeff 

p.s., note that this thinking should also be applied to any OSGi RFCs we
put forward._______________________________________________
equinox-dev mailing list
equinox-dev@xxxxxxxxxxx
https://dev.eclipse.org/mailman/listinfo/equinox-dev