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Re: [equinox-dev] boolean properties etc
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I agree that true/false values for a property/manifest header is not
future proof. In the OSGi specs we try to use multivalues so that new
values can be defined in the future.
BJ Hargrave
Senior Technical Staff Member, IBM
OSGi Fellow and CTO of the OSGi Alliance
hargrave@xxxxxxxxxx
Office: +1 407 849 9117 Mobile: +1 386 848 3788
Thomas Watson/Austin/IBM@IBMUS
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Re: [equinox-dev] boolean properties etc
We are in the process of proposing a lazy-start mechanism for the next
release of OSGi. When/If this gets added to the OSGi specification the
Eclipse-LazyStart header will not be used. Currently we are thinking of
adding a Bundle-StartPolicy header. To start with we will only specify a
"lazy" policy but this leave us open to other types of "start policies".
Jeff, is this a more acceptable approach for the header and its values?
For more details on the lazy-start policy being proposed to OSGi see
http://bundles.osgi.org/Design/LazyStart
Tom
David M Williams/Raleigh/IBM@IBMUS
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Re: [equinox-dev] boolean properties etc
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>
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09/28/2006 11:11 PM
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[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
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