Re: [Boost-users] nondynamic: A utility class that promotes safe programming
Ovanes wrote: [snip]
What do you think how this allocator will allocate the number of these element? Actually in any possible way. It can use new[] or new char[sizeof(T)*NumElems] or use an own mem-manager. And the worse thing you can't make allocator friend of your class, since users of containers can pass their own allocators. And despite all enumerated facts you will fail to compile, since the function address will fail to return the pointer to x, because it is prohibited in your case.
Yes, well boost::noncopyable also prohibits something :-) The whole intent of nondynamic is to prohibit (or make difficult) dynamic allocation/pointer usage. Do you think boost::noncopyable has a valid purpose, but nondynamic is less useful? -- Daniel
There are other classes that can't be used in containers such as scoped_ptr so there is precedent - stl containers aren't the be all and end all of software design.
Yes, well boost::noncopyable also prohibits something :-) The whole intent of nondynamic is to prohibit (or make difficult) dynamic allocation/pointer usage. Do you think boost::noncopyable has a valid purpose, but nondynamic is less useful?
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On Fri, Mar 28, 2008 at 1:59 PM, Patrick Loney < Patrick.Loney@interactivets.com> wrote:
There are other classes that can't be used in containers such as scoped_ptr so there is precedent - stl containers aren't the be all and end all of software design.
Yes, well boost::noncopyable also prohibits something :-) The whole intent of nondynamic is to prohibit (or make difficult) dynamic allocation/pointer usage. Do you think boost::noncopyable has a valid purpose, but nondynamic is less useful?
All applications of noncopyable are clearly defined in my opinion. In case of nondynamic it is not so. If I declare a class as nondynamic I still probably can assume that it is locally copyable. Isn't is so? So this construct should be valid: { //local scope std::vector<some_nondynamic> local_collection; local_collection.push_back(some_nondynamic(params_here)); // BOOM! Compiler error! new[] is not accessible or address is not accessible. ... } Do you see the problem here? Any user who deals with nondynamic must be aware of the internal structure of some third-party class involved wheather it will try to allocate storage for this class to copy it more efficiently. So in other words, you would state: I allow you to copy, but it depends how you do that... Where in noncopyable you state: I disallow any copies. IMO nondynamic will involve a whole bunche of exceptional rules when it can be used or not, where from the point of view of an automatic variable this should be valid or possible. So you break somehow natural semantics. Best Regards, Ovanes
AMDG Daniel Lidström wrote:
Ovanes wrote:
Yes, well boost::noncopyable also prohibits something :-) The whole intent of nondynamic is to prohibit (or make difficult) dynamic allocation/pointer usage. Do you think boost::noncopyable has a valid purpose, but nondynamic is less useful?
Yes. Copying objects is part of the interface of T. There are some classes for which copying does not make sense. Where T's are created is the business of users. The only even conceivable use case I see is RAII wrappers. I still don't think that it's very useful to prohibit creation on the heap, because unlike copies, C++ doesn't automatically call new for you, on the drop of a hat. In addition, trying to allocate an RAII object on the heap will not generally cause a program to go down in flames the way copying a noncopyable object can. In Christ, Steven Watanabe
participants (4)
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Daniel Lidström -
Ovanes Markarian -
Patrick Loney -
Steven Watanabe