[Boost-users] iterator adaptor not inheriting pointer typedef

Subject: [Boost-users] iterator adaptor not inheriting pointer typedef
From: Matei David (matei_at_[hidden])
Date: 2014-11-06 22:02:28

Hi,

I have some questions about the Boost Iterator library.

I've recently discovered the "hard way", meaning through impenetrable TMP 
error messages :), that when using boost::iterator_adaptor, the derived 
iterator type does not (always??) inherit the pointer typedef of the base 
iterator type. I mean, the iterator_adaptor glue class does not have this 
typedef.

So, for example, I have a Base_Iterator type with:
Base_Iterator::pointer != Base_Iterator::value_type*

If I do:
class Derived_Iterator : public boost::iterator_adaptor< Derived_Iterator, 
Base_Iterator > {...}

then, strangely I find:
Derived_Iterator::value_type == Base_Iterator::value_type (OK)
Derived_Iterator::pointer == Base_Iterator::value_type* != 
Base_Iterator::pointer (not OK)

I looked at the documentation, and I did find a mention of this, but only 
for iterator_facade, here:
http://www.boost.org/doc/libs/develop/libs/iterator/doc/iterator_facade.html

The corresponding page for iterator_adaptor does not mention the pointer 
typedef at all. While for facade using a plain pointer seems ok (no other 
reasonable default), I would argue that for adaptor this is not ok. Is this 
expected behaviour or a bug?

Within the same setting, and in what could be a related issue, I also found 
that the intermediate boost::iterator_adaptor<> class does not seem 
to contain the default/common sense definition:
Base_Iterator operator->() const { return this->base(); }

I didn't look inside the source code of boost::iterator_adaptor, but I 
found a situation where I have to put this definition explicitly inside 
Derived_Iterator for my code to compile (without it, it doesn't). Does 
this sound like expected behaviour?

Thanks
M