Boost Users :
Subject: Re: [Boost-users] Ranges to Collections
From: John M. Dlugosz (mpbecey7gu_at_[hidden])
Date: 2011-06-07 10:25:51
On 6/6/2011 9:31 PM, ÇÇÖ¾Ç¿ qiaozhiqiang-at-leadcoretech.com wrote:
> Maybe you want make_vector() , make_list().
> template<class T, class SinglePassRange>
> T make_container(const SinglePassRange& from)
> T c;
> boost::push_back(c, from);
> return move(c);
I think it would be better to make use of the two-iterator form of the constructor rather
than calling push_back. That way it can allocate storage for all elements in advance if
the kind of range allows for finding the difference easily.
return T (from.begin(), from.end());
I guess your way optimizes for the case where it needs to slowly traverse the range in
order to find the end() first. I suppose boost::push_back does something similar if it
can, but it still constructs as zero size and then resizes.
> template<class SinglePassRange>
> std::vector<typename SinglePassRange::value_type> make_vector(const SinglePassRange& from)
> return make_container<std::vector<typename SinglePassRange::value_type>>(from);
The make_container needs to be told the exact container type in the call, and your
make_vector et al. is a different name for each possible container. I would think you
could use a template template argument and pass in the container species only, and have it
obtain the value_type for itself. I think that would be good enough, as the details of the
value types is the hard part.
But, I speculate that a simple expression could figure out the complete type by itself via
using a templatized conversion operator.
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