On 9/21/2011 8:21 PM, Jesse Phillips wrote:
On Wed, 21 Sep 2011 10:15:31 -0700, Mehrdad wrote:
I can't find the thread, but I remember someone (bearophile?) mentioned
that the reason we have transitive const is to support purity.
I don't think I understand why this is necessary, though -- could
someone please explain why we have transitive const, and what problems
it fixes?
Thanks!
I came across this blog earlier, it may hold the answers you seek:
http://www.reddit.com/tb/kkwch
"One of the core difficulties in concurrent programming is trying to
avoid the simultaneous reading and writing of data. Like with functional
programming, concurrent programming is a lot easier when data can't
change -- if you have no writes then you can't possibly have
simultaneously reading and writing. However, unlike functional
programming, logical const just doesn't cut it. If you were to give a
reference to an instance of my Matrix class to two threads, and ask them
both to compute the determinant then you could end up with an ugly race
condition due to the memory writes in the caching mechanism. Here,
physical immutability really does matter."
I don't see why immutability has anything to do with constness... would
you mind clarifying? Why does having transitive immutable also imply
that we /must/ have transitive const?
