Terry Reedy wrote:
On 2/16/2010 3:15 PM, John Nagle wrote:
In the beginning, Python had some types which were "frozen",
> and some which weren't.
In the beginning, there was only one 'frozen' general purpose collection
type, the tuple. And Guido resisted the suggestion that lists and tuple
were mutable and frozen versions of each other.
However, things have changed, and lists and tuple *are* effectively
mutable and hashable versions of each other, and we have the three other
pairs you mentioned. The idea of freeze() may have been floated (and
punctured) during Py3 discussions, but I think it a fairly good one.
Yes, we're now at the point where all the built-in mutable types
have "frozen" versions. But we don't have that for objects. It's
generally considered a good thing in language design to offer,
for user defined types, most of the functionality of built-in ones.
It's the concurrency aspect of this that interests me, though.
A language with immutable objects can potentially handle concurrency
more safely than one where everything is potentially mutable.
The language knows what can't change, which simplifies locking.
John Nagle
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