Re: OK, maybe so

Post #101,728 by JimWeirich 5/13/03 6:13:40 PM Reply	Re: OK, maybe so ToddBlanchard: [...] figure out how you put a null integer into the container in the first place. How about (stealing the example from the article) ... Map<String, Integer> m = new TreeMap<String, Integer>();\nint i = m.get("not_yet_in_map"); Should "i" be zero, or should there be a null pointer exception thrown? (remember that `get` returns a null pointer of the key doesn't exist). -- -- Jim Weirich jweirich@one.net [link\|http://w3.one.net/~jweirich\|http://w3.one.net/~jweirich] --------------------------------------------------------------------- "Beware of bugs in the above code; I have only proved it correct, not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)
Post #101,729 by tuberculosis 5/13/03 6:21:26 PM Reply	Well in this case I think a KeyNotFoundException should be thrown. This is just another case where Smalltalk's collection class protocols are vastly superior to J-crap. i := dict at: 'not_there' ifAbsent: [ 0 ]. For java I would propose something similar on Map. map.getValueIfAbsent('key_not_found',5); failure to use this should throw a KeyNotFoundException. "Packed like lemmings into shiny metal boxes. Contestants in a suicidal race." - Synchronicity II - The Police
Post #101,736 by JimWeirich 5/13/03 7:16:46 PM Reply	Perhaps ... but ... Todd: For java I would propose [...] map.getValueIfAbsent('key_not_found',5); That's an interesting proposal ... but it still doesn't solve the basic question of unboxing nulls. But ... let's let the J-Heads worry about that. Ruby handles missing hash values a bit differently. If the key is not in the hash, you get a default value (which is typically nil, but can be something else). h = Hash.new\n h['not_there'] #=> nil\n\n g = Hash.new { 0 }\n g['not_there'] #=> 0\n\n j = Hash.new { fail "key not found" }\n j['not_there'] #=> Exception -- -- Jim Weirich jweirich@one.net [link\|http://w3.one.net/~jweirich\|http://w3.one.net/~jweirich] --------------------------------------------------------------------- "Beware of bugs in the above code; I have only proved it correct, not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)
Post #102,309 by tuberculosis 5/16/03 3:57:14 PM Reply	My point was it should be impossible to "box" null (and I think it probably is). So the problem ought not to exist. So the problem isn't how do you unbox null, its "how do you provide a mechanism for signaling and handling this case". I have found the requirement to provide a default "not found" value to be a useful bit of flypaper. OTOH, Java currently returns null from maps where the key is missing so I suppose they will decide that backwards compatibility is more important than better behvior. "Packed like lemmings into shiny metal boxes. Contestants in a suicidal race." - Synchronicity II - The Police

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