Steven D'Aprano wrote:
On Fri, 25 Mar 2011 10:21:35 +0100, Antoon Pardon wrote:
On Thu, Mar 24, 2011 at 11:49:53PM +0000, Steven D'Aprano wrote:
On Thu, 24 Mar 2011 17:47:05 +0100, Antoon Pardon wrote:
However since that seems to be a problem for you I will be more
detailed. The original poster didn't ask for cases in which cmp was
necessary, he asked for cases in which not using cmp was cumbersome.
I'm the original poster, and that's not what I said. I said:
"If anyone has any use-cases for sorting with a comparison function
that either can't be written using a key function, or that perform
really badly when done so, this would be a good time to speak up."
You'll notice that I said nothing about whether writing the code was
easy or cumbersome, and nothing about readability.
Well fine. I should have realised the question was just a pretense and
that there really never was any intention to consider the reactions,
because the answer is already fixed. Of course a key function can always
be written, it may just need a specific class to implement the specific
order. Likewise there is no reason to expect the order-functions to
preform worse when implemented in a class, rather than in a function.
The reason Guido is considering re-introducing cmp is that somebody at
Google approached him with a use-case where a key-based sort did not
work. The use-case was that the user had masses of data, too much data
for the added overhead of Decorate-Sort-Undecorate (which is what key
does), but didn't care if it took a day or two to sort.
So there is at least one use-case for preferring slowly sorting with a
comparison function over key-based sorting. I asked if there any others.
It seems not.
That was known from the begining, was it ? Since key sort trades memory
for CPU, you could expect that "masses of data" use cases may fail
because of memory shortage.
JM
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