Ranged Base For Loop requires a Call Operator, C++ (clang)

Language: Layout:

//clang 3.7.0

#include <iostream>

template<class Real>
class RowIterator {
public:
	RowIterator() { }
	RowIterator(Real* begin, size_t rows, size_t cols) : begin(begin), rows(rows), cols(cols) { }

Real* operator*() const { return begin; }
	Real& operator[](size_t col) const { return begin[col]; }

bool operator!=(const RowIterator& it) const { return begin != it.begin; }
	RowIterator& operator++() { begin += cols; --rows; return *this; }

private:
	Real* begin;
	size_t rows, cols;
};

namespace range
{

template<class Iterator>
struct Range {
	Iterator begin, end;
	Range() { }
	Range(Iterator begin, Iterator end) : begin(begin), end(end) { }
};

template<class Iterator>
Iterator begin(const Range<Iterator>& range) { return range.begin; }
template<class Iterator>
Iterator end(const Range<Iterator>& range) { return range.end; }

}

using range::Range;
template<class Iterator>
Range<Iterator> make_range(Iterator begin, Iterator end) { return Range<Iterator>(begin, end); }

Range<RowIterator<float>> make_row_range(float* mat, size_t rows, size_t cols) {
	return make_range(
		RowIterator<float>(mat, rows, cols),
		RowIterator<float>(mat + rows * cols, 0, cols));
}

int main() {
	size_t rows = 4, cols = 6;
	float* mat = new float[rows * cols];
	for(size_t i = 0; i < rows * cols; ++i)
		mat[i] = (float)i;
	auto rowrange = make_row_range(mat, rows, cols);
	std::cout << "begin, end" << std::endl;
	for(auto b = begin(rowrange), e = end(rowrange); b != e; ++b)
		std::cout << "start of row: " << b[0] << std::endl;
	{
        std::cout << "reference implementation" << std::endl;
		auto && __range = make_row_range(mat, rows, cols);
		for (auto __begin = begin(__range), __end = end(__range); 
			__begin != __end; ++__begin) { 
			auto range_declaration = *__begin; 
			std::cout << "start of row: " << range_declaration[0] << std::endl;
		}
	}
#if 1
	std::cout << "range based" << std::endl;
	for(auto row : rowrange) // row : float*
		std::cout << "start of row: " << row[0] << std::endl;
#endif
	return 0;
}

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Compilation time: 0.52 sec, absolute service time: 0,66 sec