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Posted to dev@commons.apache.org by "Stephen Colebourne (JIRA)" <ji...@apache.org> on 2006/12/29 19:29:22 UTC
[jira] Commented: (LANG-283) Visitors for Builders
[ http://issues.apache.org/jira/browse/LANG-283?page=comments#action_12461426 ]
Stephen Colebourne commented on LANG-283:
-----------------------------------------
This looks very clever, but is probably beyond that which the builders were originally intended for.
> Visitors for Builders
> ---------------------
>
> Key: LANG-283
> URL: http://issues.apache.org/jira/browse/LANG-283
> Project: Commons Lang
> Issue Type: New Feature
> Affects Versions: 2.2
> Environment: Any
> Reporter: Aldrin Leal
> Priority: Trivial
> Fix For: 3.0
>
> Attachments: visitors.patch
>
>
> While doing commons-lang stuff, I found the repetitive nature of
> Builder stuff. Therefore, i decided to:
> a) Create a SingleBuilder (for ToString / HashCode) and a
> DualBuilder (CompareTo / Equals) interface, and make their classes
> implementing;
> b) Create a SingleBuilderVisitor and DualBuilderVisitor;
> c) Do the proper wiring, while creating new constructors using the visitors;
> d) Create new tests and ensuring javadoc plays nice along;
> There's a patch attached in this e-mail, done against the latest
> svn STABLE url for 2.2
> (http://svn.apache.org/repos/asf/jakarta/commons/proper/lang/branches/LANG_2_2_X/)
> There might be errors, but methinks it's a great idea to declare a
> constant like this in your source code.
> private static final EQUALS_VISITOR = new DualBuilderVisitor() {
> public void visit(DualBuilder builder, Object lhs, Object rhs) {
> Type lhsObj = (Type) lhs;
> Type rhsObj = (Type) rhs;
> builder.append(lhsObj.getId(),
> rhsObj.getId()).append(lhsObj.getName(), rhsObj.getName());
> }
> };
> And then, declare and instantiate builders like as, say:
> public boolean equals(Object anotherObj) {
> return new EqualsVisitor(EQUALS_VISITOR, this, anotherObj);
> }
> Please note this implementation, overrall, also lets you easily use
> a single visitor for either equals and compareto, thus creating a
> single point of management for all your
> field-maintenance-in-value-objects-needs.
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