Use covariant clone() return types
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Key: LUCENE-2000
URL: https://issues.apache.org/jira/browse/LUCENE-2000
Project: Lucene - Java
Issue Type: Task
Affects Versions: 3.0
Reporter: Uwe Schindler
Attachments: LUCENE-2000-clone_covariance.patch
*Paul Cown wrote in LUCENE-1257:*
OK, thought I'd jump in and help out here with one of my Java 5 favourites.
Haven't seen anyone discuss this, and don't believe any of the patches address
this, so thought I'd throw a patch out there (against SVN HEAD @ revision
827821) which uses Java 5 covariant return types for (almost) all of the
Object#clone() implementations in core.
i.e. this:
public Object clone() {
changes to:
public SpanNotQuery clone() {
which lets us get rid of a whole bunch of now-unnecessary casts, so e.g.
if (clone == null) clone = (SpanNotQuery) this.clone();
becomes
if (clone == null) clone = this.clone();
Almost everything has been done and all downcasts removed, in core, with the
exception of
Some SpanQuery stuff, where it's assumed that it's safe to cast the clone() of
a SpanQuery to a SpanQuery - this can't be made covariant without declaring
"abstract SpanQuery clone()" in SpanQuery itself, which breaks those SpanQuerys
that don't declare their own clone()
Some IndexReaders, e.g. DirectoryReader - we can't be more specific than
changing .clone() to return IndexReader, because it returns the result of
IndexReader.clone(boolean). We could use covariant types for THAT, which would
work fine, but that didn't follow the pattern of the others so that could be a
later commit.
Two changes were also made in contrib/, where not making the changes would have
broken code by trying to widen IndexInput#clone() back out to returning Object,
which is not permitted. contrib/ was otherwise left untouched.
Let me know what you think, or if you have any other questions.
[ Show ยป ] Paul Cowan added a comment - 21/Oct/09 03:01 AM OK, thought I'd jump
in and help out here with one of my Java 5 favourites. Haven't seen anyone
discuss this, and don't believe any of the patches address this, so thought I'd
throw a patch out there (against SVN HEAD @ revision 827821) which uses Java 5
covariant return types for (almost) all of the Object#clone() implementations
in core. i.e. this: public Object clone() { changes to: public SpanNotQuery
clone() { which lets us get rid of a whole bunch of now-unnecessary casts, so
e.g. if (clone == null) clone = (SpanNotQuery) this.clone(); becomes if (clone
== null) clone = this.clone(); Almost everything has been done and all
downcasts removed, in core, with the exception of
Some SpanQuery stuff, where it's assumed that it's safe to cast the clone() of
a SpanQuery to a SpanQuery - this can't be made covariant without declaring
"abstract SpanQuery clone()" in SpanQuery itself, which breaks those SpanQuerys
that don't declare their own clone()
Some IndexReaders, e.g. DirectoryReader - we can't be more specific than
changing .clone() to return IndexReader, because it returns the result of
IndexReader.clone(boolean). We could use covariant types for THAT, which would
work fine, but that didn't follow the pattern of the others so that could be a
later commit.
Two changes were also made in contrib/, where not making the changes would have
broken code by trying to widen IndexInput#clone() back out to returning Object,
which is not permitted. contrib/ was otherwise left untouched. Let me know what
you think, or if you have any other questions.
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