Always keep a field for private[this] var class parameters
#9226
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I'm personally in favor of the simpler solution, always keep the field. Even dotty agrees |
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On one of the PRs, I mention that doti doesn't do it, but it wasn't clear what "inferred |
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I agree there is not much benefit in this secret handshake. If user doesn't want a field, they should change their code. The possible use case was if class var param was mutated only during constructor, but otherwise unused. The test fail is that neg/t1503 with Nil.type. |
som-snytt
approved these changes
Sep 27, 2020
Reads of `var` class parameters in the constructor are not rewritten to the constructor parameter, they keep referring to the field to ensure potential field writes are reflected (this was fixed in scala#7688). This means that the corresponding field cannot be elided even if it's never written. The alternative solution would be to detect `private[this] var` fields that are only read in the constructor. However this is difficult to implement, see scala#9143.
After the previous commit, the field for a `private[this] var` class parameter is only elided if the field is not used at all. This seems not to be worth the effort.
👍 but you can't do that with method parameters either, so no big loss and in a way it makes things more regular |
private[this] var class parameter fields that are only readprivate[this] var class parameters
This was referenced Oct 22, 2020
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Reads of
varclass parameters in the constructor are not rewritten tothe constructor parameter, they keep referring to the field to ensure
potential field writes are reflected (this was fixed in #7688).
This means that the corresponding field cannot be elided even if it's
never written.
The alternative solution would be to detect
private[this] varfieldsthat are only read in the constructor. However this is difficult to
implement, see #9143.
The second commit goes a step further by never eliding the field
for a
private[this] varclass parameter. Up for discussion.Fixes scala/bug#12002 (the remaining part).
This needs to be backported to 2.12.x.