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From: Joshua Cranmer <Pidgeot18@verizon.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: Refactoring discovery
Date: Wed, 30 Mar 2011 17:31:53 -0400
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On 03/30/2011 04:10 PM, David Lamb wrote:
> We already write "combined operations" in other contexts.
> if (x.hasKey(y)) then x.addPair(y,
> someVeryBigThingIDidn'tWantToSysnthesizeUnlessIHadTo)

Well, another way to implement this is:

public boolean hasKey(Y y) {
   LocPtr ptr = getWhereToInsert(y);
   this.cachedPtr = ptr;
   return ptr.valid();
}

public void addPair(Y y, Object obj) {
   LocPtr ptr;
   if (cachedPtr && cachedPtr.y == y)
     ptr = cachedPtr;
   else
     ptr = getWhereToInsert(y);
   ptr.insert(obj);
}

Which pretty much gets you the "benefit" of combining them into one 
single operation without needing to provide all of the back-level 
predicate code operations (set-if-present, set-if-not-present, etc.)
-- 
Beware of bugs in the above code; I have only proved it correct, not 
tried it. -- Donald E. Knuth