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https://issues.apache.org/jira/browse/LANG-1084?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14295414#comment-14295414
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Sebb commented on LANG-1084:
----------------------------
Not sure that is going to be very usable, as the API is assymetric.
For example:
{code}
Integer i = 1;
Number n = i;
Test.equalT(n, i);
Test.equalT(i, n); // Compiler error
{code}
The contract of equals() requires symmetry; this is not symmetric.
I don't think it makes sense to try to bundle type checking into the equals
method.
Although the proposed method will detect some changes of return type, it won't
detect them all - e.g. both getPersonViaX() and getPersonViaY() are both
changed to a different mutually compatible type.
Sorry, but I don't think this belongs in LANG
> ObjectUtils should have type-safe equals() method
> -------------------------------------------------
>
> Key: LANG-1084
> URL: https://issues.apache.org/jira/browse/LANG-1084
> Project: Commons Lang
> Issue Type: Improvement
> Reporter: Thibault Kruse
> Priority: Minor
>
> Commonly implementation of Object.equals() perform an instanceof check before
> casting and then comparing properties.
> That means that any code like a.equals(b) does not imply any compile-time
> type checking.
> However it can be very desirable to check types at compiletime in many
> (though not all) situations. E.g. consider this code:
> Person a = getPersonViaX();
> Person b = getPersonViaY();
> assert !a.equals(b);
> this code is typesafe at compiletime. If getPersonViaY() changes the return
> type to something that does not extend Person, this will fail to compile.
> Now consider this refactored:
> assert !getPersonViaX().equals(getPersonViaY());
> In this case the change to getPersonViaY() would go unnoticed, both at
> compiletime AND at runtime (if equals merely returns false in the instanceof
> check of the most common equals method design).
> Based on this blogpost:
> http://rickyclarkson.blogspot.de/2006/12/making-equalsobject-type-safe.html
> I suggest a typesafe equals method for situations like above:
> public static <T,U extends T> boolean equalT(T t,U u)
> { return t.equals(u); }
> and possible a typesafe notEquals method as well.
> I am dispassionate about naming of the method, might as well be
> typeSafeEquals() or whatever fits best into apache commons.
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