--- Gregory Colvin <[EMAIL PROTECTED]> wrote:Yep. I still think UserAllocator is a good default, and that where it doesn't suffice there is some value to playing nicely with STL.
So even when we come up with some beautiful new thing to do the allocation job better, we will still need adaptors both ways, so that one can get an allocator from an STL container and turn it in to one of our new things, or take one of our new things and turn it into an allocator to use in an STL container.
Am I right in trying to summarize your suggestion about UserAllocator?
If you want to parametrize how a boost class manages memory, use UserAllocator parameter.
Unless you need the standard Allocator interface.
1. The allocator parameter should implement the UserAllocator interface.
2. All instances of UserAllocator must be equal and stateless.
The Boost pools use UserAllocator only as a type parameter. It is not required to be constructible or comparable.
3. If your class is using STL containers, use boost::memory::allocator adapter (see bellow).
Why not just use std::allocator?
4. To construct/destroy objects, use boost::memory::construct/destroy.
See below.
5. Avoid using explicit references to allocators.
... Usage example:
==============
template< typename T, typename UserAllocator = boost::default_user_allocator_new_delete >
class X
{
What if you want X to use the same allocator as some other STL container constructed with a non-Boost allocator? That would be difficult unless you have
template<typename T, class StdAllocator = std::allocator<T> >
struct X {
X(const StdAllocator&);Also, it might sometimes be desirable, as it is for shared_ptr, to defer the choice of allocator until construction time:
template<typename T>
struct X {
template<class StdAllocator = std::allocator<T> >
X(const StdAllocator&);Or, if UserAllocator suffices:
template<typename T>
struct X {
template<class UserAllocator> X();T* _p;
Leading underscores are a no-no.
std::vector<T, boost::memory::allocator<T, UserAllocator> > _v;
X() { _p = boost::memory::construct<T, UserAllocator>( 1 )
How to pass arguments to T's constructor? Better just
p = new(UserAllocator::malloc(sizeof T)) T(...)
}
~X()
{
if( _p )
boost::memory::destroy<T, UserAllocator>( _p, 1 );
In which case, why not just
p->~T(), UserAllocator::free(p);
?
} };
Eugene
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