macOS parallel for each

for_each.h

#pragma once

#include <iterator>
#include <utility>

#include "dispatch/dispatch.h"
template<typename It, typename F>
void parallel_for_each(It a, It b, F&& f)
{
    size_t count=std::distance(a,b);
    using data_t=std::pair<It,F>;
    data_t helper=data_t(a,std::forward<F>(f));
    dispatch_apply_f(count, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), &helper, [](void* ctx,size_t cnt)
    {
        data_t* d=static_cast<data_t*>(ctx);
        auto elem_it=std::next(d->first,cnt);
        (*d).second(*(elem_it));
    });
}