On Sat, Sep 18, 2010 at 10:37 AM, TONGARI wrote:

2010/9/17

...

It seems like there ought to be a natural way to do this using an iterator class.

I don't think that'll be a good solution to this problem, not efficient enough.

Whether it's efficient "enough" really depends on the OP's requirements. However, if you're worried about efficiency you should look up Matt Austern's 1998 paper "Segmented Iterators and Hierarchical Algorithms" -- Dave Abrahams BoostPro Computing http://www.boostpro.com

I have the same problem, to view a map (k1->k2->v) as a sequence(k1, k2) -> v. With iterator_facade and iterator_transform, the problem solved verbosely. in the code, Begin and End is unary functors applied to first iterator to get second begin, end iterator. template class chain_iter : public boost::iterator_facade< chain_iter, std::pair, Tag, std::pair > { public: typedef F first_type; typedef S second_type; typedef std::pair value_type; typedef value_type reference; // no, no reference to temporary chain_iter() {} chain_iter(const F &f, const F &f_end, const S &s) : m_first(f), m_first_end(f_end), m_second(s) { normalize(); } chain_iter(const chain_iter &r) : m_first(r.m_first), m_first_end(r.m_first_end), m_second(r.m_second) { normalize(); } private: friend class boost::iterator_core_access; void normalize() { while (m_first != m_first_end && m_second == End()(m_first)) { ++m_first; if (m_first != m_first_end) m_second = Begin()(m_first); } } void increment() { assert(m_first != m_first_end); ++m_second; normalize(); } void decrement() { while (m_second == Begin()(m_first)) { --m_first; m_second = End()(m_first); } --m_second; } reference dereference() const { return std::make_pair(m_first, m_second); } bool equal(const chain_iter &r) const { if (m_first == m_first_end) { return r.m_first == r.m_first_end; } return m_first == r.m_first && m_second == r.m_second; } F m_first; F m_first_end; S m_second; }; Changsheng Jiang On Sun, Sep 19, 2010 at 22:57, Richard

wrote:

[Please do not mail me a copy of your followup]

boost-users@lists.boost.org spake the secret code thusly:

...

On Sat, Sep 18, 2010 at 10:37 AM, TONGARI wrote:

...

2010/9/17

...

It seems like there ought to be a natural way to do this using an

iterator

...

...

class.

I don't think that'll be a good solution to this problem, not efficient enough.

Whether it's efficient "enough" really depends on the OP's requirements. However, if you're worried about efficiency you should look up Matt Austern's 1998 paper "Segmented Iterators and Hierarchical Algorithms"

It was an interesting read and not hard to implement.

http://lafstern.org/matt/segmented.pdf -- "The Direct3D Graphics Pipeline" -- DirectX 9 draft available for download http://legalizeadulthood.wordpress.com/the-direct3d-graphics-pipeline/

Legalize Adulthood! http://legalizeadulthood.wordpress.com

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