I was having some problems in an abandoned prototype with incomplete
types, I'm not sure I will have this problem now, but I'm keeping this
anyway, as it seems useful.
The current organisation of the headers has been making less and less
sense over the years, so to simplify things, I'm just going to combine
them into a single header. This change will make it easier to do that.
Warning is:
allocate.hpp:335:19: warning: conversion to ???unsigned int??? from
???long unsigned int??? may alter its value [-Wconversion]
I'm not sure, but I think it's because the sizeof is a long unsigned
int, and the template parameter is an unsigned int. The sizeof isn't
even used, it's just there to get a value for expression SFINAE.
FWIW the standard says that equality is undefined behaviour if the Hash
and Pred function objects behave differently. But I think we should
support different hash functions, e.g. so that randomized hash functions
will work.
Which is to some extent going in circles, as this is how the containers
were originally implemented. But I think this is cleaner. It also fixes
a minor problem where the internal and external iterator types are
different for some containers, as the external iterators are all const.
Currently just storing the value without a const. Can do better with
C++11 constructors, so maybe should do that, and cast away const on
compilers without support.
Another problem is that std::allocator<const int> doesn't compile for
libstdc++ (and potentially other standard libraries), so
boost::unordered_set<const int> can't compile. I'm not sure if I should
work around that, as it means changing the type of the container
(i.e. to boost::unordered_set<const int,... , std::allocator<int>>).
std::allocator::construct uses a C-style cast to void pointer, so it can
accept const pointers, but allocator_traits::construct uses a static_cast
by default, so const pointers don't work. This means the implementation
needs to cast away const when constructing members of a std::pair. This
wouldn't happen if piecewise construction was used, as the members could
be constructed normally.
The hash and key equality functions were assigned before allocating new
buckets. If that allocation failed, then the existing elements would be
left in place - so if accessed after the exception they could be in the
wrong buckets or equivalent elements could be incorrectly grouped
together.
AFAICT it's not needed since the construct arguments and the members are
the same reference type. Maybe it was for older compilers? And it appears
to be causing issues with string literals in older versions of Visual
C++.
Daniel James