[TAP5-2658] Tuple should implement hashCode based on its values

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 5.6.2, 5.7.0
• Component/s: tapestry-func
• Assignee: Ben Weidig
• Reporter: Ben Weidig
• Created: 06/Jan/21 12:27
• Updated: 11/Feb/21 21:37
• Resolved: 11/Feb/21 21:37

Description

Summary

The class `org.apache.tapestry5.func.Tuple<A, B>` overrides `boolean equals(Object)` to check equality of its values.
But it doesn't provide an appropriate `int hashCode()` implementation, thereby violating a base contract of Java objects, leading to undefined behavior depending on someone using the hash code value.

Risks and Assumptions

Minimal risk is assumed.
Usage in HashMaps, or other hash code related structures/methods might behave differently.
But due to the previously broken contract, it should affect code using it "wrong".

Alternatives

Deprecating Tuple, and providing a new implementation.

Details of Proposed Changes

Add `hashCode()` based on `java.util.Objects.hash(Object...)`.
Add tests for `hashCode()`.

Code is already implemented and ready to be committed and pushed, if change is accepted.