On Sun, Mar 4, 2018 at 5:22 AM, Richard Damon <rich...@damon-family.org> wrote: > On 3/3/18 12:43 PM, Chris Angelico wrote: >> >> On Sun, Mar 4, 2018 at 4:37 AM, Richard Damon <rich...@damon-family.org> >> wrote: >>> >>> On 3/3/18 11:33 AM, Michael Torrie wrote: >>>> >>>> On 03/03/2018 09:02 AM, ooom...@gmail.com wrote: >>>>> >>>>> I can assure you that RAII does what it says on the tin and is relied >>>>> on >>>>> in >>>>> many critical systems to release resources robustly ... given the >>>>> pre-requisite deterministic destruction. >>>> >>>> Sure but did you read what Paul Moore wrote? He said RAII works in C++ >>>> because objects are allocated on the *stack* with strict lifetimes and >>>> scopes. They won't ever have cycles and they are guaranteed to be >>>> destroyed no matter what as the stack is unwound. Python has no >>>> stack-allocated objects. >>>> >>>> In C++, Heap-allocated objects must still be managed manually, without >>>> the benefit of RAII, for much of the same reasons as people are giving >>>> here for why RAII is not a good fit for Python. There are smart pointer >>>> objects that try to give RAII semantics to heap-allocated objects, with >>>> varying degrees of success. In other words there are some limitations. >>>> >>>> Python does not have stack-allocated objects, so the same issues that >>>> prevent RAII from automatically applying in C++ to heap objects exist >>>> here. >>> >>> >>> Yes, stack allocated object in C++ have a nice lifetime to allow RAII to >>> work, but it doesn't just work with stack allocated objects. A lot of >>> RAII >>> objects are members of a class object that may well be allocated on the >>> heap, and RAII makes sure that all the needed cleanup gets done when that >>> object gets destroyed. >> >> How do you guarantee that the heap object is properly disposed of when >> you're done with it? Your RAII object depends 100% on the destruction >> of the heap object. >> >> ChrisA > > > Yes, the heap object 'owns' a resource, and as long as that heap object > exists, the resource needs to exist, but as soon as it doesn't, you want > that resource freed. > > That heap object might well be controlled by some other RAII object (maybe a > smart pointer with a ref count) or maybe that object is being manually > controlled by the program. But the key is that when it goes away, all of the > resources it controls via RAII are automatically cleaned up, and you don't > need all that cleanup made explicit in the owning class.
You're trying to handwave away the *exact point* that we are all making: EVERY object in Python is a heap object. So how is your magic wand going to make any of this work? You have to do it exclusively with heap objects because there is nothing else available. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
