I was looking around the Clojure source code and noticed that the
persistent immutable collections caches their hash codes.
The java doc says the following about the equals method: (http://
download.oracle.com/javase/1.4.2/docs/api/java/lang/Object.html)
"If two objects are equal according to the equals(Object) method, then
calling the hashCode method on each of the two objects must produce
the same integer result."
So I was thinking, wouldn't it be possible to use the cached hash code
to rule out cases of equals where equals returns false?
public boolean equals(Object obj){
...
if (_hash != -1 && hashCode() != obj.hashCode()) {
return false;
}
...
}
This might of cause result in an extra call to hashCode(), so I don't
know if it is worth it.
Maybe some internal functionality could be added, to ask the
collections if their hash code has been cached.
What are your thoughts?
Kind regards Sune Simonsen
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