On Sunday, 4 March 2018 03:16:31 UTC, Paul Rubin wrote: > Chris Angelico <ros...@gmail.com> writes: > > Yep, cool. Now do that with all of your smart pointers being on the > > heap too. You are not allowed to use ANY stack objects. ANY. Got it? > > That's both overconstraining and not even that big a problem the way you > phrase it. > > 1) Python has both the "with" statement and try/finally. Both of these > run code at the exit from a syntactically defined scope. So they are > like stack allocation in C++, where a deallocator can run when the scope > exits. > > 2) Even with no scope-based de-allocation, it's common to put smart > pointers into containers like lists and vectors. So you could have a > unique_ptr to a filestream object, and stash the unique_ptr someplace as > a vector element, where the vector itself could be part of some even > more deeply nested structure. At some point, the big structure gets > deleted (maybe through a manually-executed delete statement). When that > happens, if the nested structures are all standard containers full of > unique_ptrs, the top-level finalizer will end up traversing the entire > tree and freeing up the file handles and whatever else might be in > there. > > It occurs to me, maybe #2 above is closer to what the OP is really after > in Python.
Yep. C++ smart pointers are a good analogue to python references for purposes of this PEP. > I guess it's doable, but refcounts don't seem like the right > way. Well refcounts are definitely "doable": This is how the reference python implementation, CPython, currently manages to comply with this PEP and can therefore be used for RAII. This PEP is an attempt to _guarantee_ this behaviour and make the elegance of RAII available to all pythonistas that want it. Without this guarantee python is not attractive to applications that must manage non-trivial resources reliably. Aside: I once read somewhere that must have seemed authoritative at the time, that CPython _guarantees_ to continue to behave like this - but now the subject is topical again I can find no trace of this guarantee. -- https://mail.python.org/mailman/listinfo/python-list
