Question

I admit I had difficulties coming up with a reasonable description for this. I cannot think of a good term that would describe precisely what I’m looking for. Perhaps this could be called a slicing iterator.

Let’s say I have something like this:

struct S
{
    int i;
    char *s;
    float f;
};

std::vector<S> v(10);

What I’m looking for is a way to construct an iterator, that would point to a member of S. I’d like to be able to pass it to something like std::min_element without creating a predicate in each case. Something that might look like this:

std::min_element(slicing_iterator(v.begin(), S::f), slicing_iterator(v.end(), S::f));

Is there any template trick that I could use to achieve this? Or perhaps it’s already done somewhere in Boost or some other library?

Answer 1

If you’re looking for an iterator that converts S into its S::f, this could certainly be done using boost (what can’t be?):

std::cout << *std::min_element(
               boost::make_transform_iterator(v.begin(), boost::bind(&S::f, _1)),
               boost::make_transform_iterator(v.end(), boost::bind(&S::f, _1))
              ) << '\n';

test: https://ideone.com/jgcHr

But if you’re looking for the S whose S::f is the smallest in the vector, the predicate is the most reasonable approach.