My version of the PGI compiler was having problems with using
IteratorFromArrayPortal with STL algorithms. I traced the problem to
iterator_facade checking to see if the reference type we gave it was
a real reference (e.g. T&). It is not, iterator_facade downgraded the
iterator trait to a simple input iterator tag even though I declared
it with a random access traversal. I don't know what the reference type
has to do with random access, but in any case the value object is
designed to behave like a reference in that when you assign to it
the value gets propagated to the array. To tell boost this is the case,
I made a specialization of boost::is_reference that declares the
value type as a reference.
I'm not sure why it failed for me but not elsewhere. It might be that
this version of the PGI compiler is using "old-style" iterator traits
whereas other were using newer style that matches better the boost
iterator traits that iterator_facade is actually using.
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