do you know more about the logic in the order those hashing routines sort the data

There is no ordering principle in Perls hash implementation. In fact the hashes are statically initialized with a pseudorandom sequence at launch. The order that follows from there is strictly incidental to anything else. The only thing that you are currently promised is that you will get the same sequence from the same set of keys that were inserted into the structure. (This is order dependent. Change the order in which you insert keys into the hash, and the output sequence will differ as well.)

And get this: Its going to get worse. There is a DOS attack that is based around targetting vulnerabilities in the hash algorithm causing perl to slow to a crawl while populating the hash. In order to resolve this the hash will no longer be initialized with a static pseudorandom sequence, instead it will be initialized with dynamic pseudo random sequence. Thus there will be no guaranty that the same set of inserts will produce the same order of keys on two different runs.

The moral of this story is that if you want your code to be forward compatible with later versions of perl then you had better not depend on native key order in any way at all. If you need to do this then sort the keys.

It should come to no suprise to people that there is lots of code out there that will be subtly broken by this change. People depend on the repeatability of hash keys more often than they think they do.

Just a question on this, because I can't be bothered to dig it out myself. Will something the following still work as expected?

my %new_hash;

@new_hash{map munge($_), keys %old_hash} = value %old_hash;
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This depends on the sequence of elements returned being identical and is the only way I ever depend on order in a hash.

Makeshifts last the longest.

From perlfunc:keys

The actual random order is subject to change in future versions of perl, but it is guaranteed to be the same order as either the values or each function produces (given that the hash has not been modified).

As far as I'm aware, the only way to iterate the values of a hash (internally), is to iterate the keys and use them to retrieve the values, so unless an extra step was added to randomise them after retrieval, the returns from keys and values (and each) would have to come back in the same order?

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"Efficiency is intelligent laziness." -David Dunham
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