serengti / cpp_iterzip

Header-only C++17 implementation for a python-style zip iterator.

iterzip for C++17

Header-only implementation for a python-style zip iterator. Simplifies iteration over multiple containers at once. Supports all standard iterator categories and conforms to std::iterator_traits.

Usage

Supports all iterator-conforming containers. This, of course, includes all STL containers such as std::array, std::vector, std::list etc. You can zip arbitrary many containers and iterate them all at once!

#include "iterzip.hpp"
using iterzip::zip;

std::array<int, 5> a{1,2,3,4,5};
std::array<int, 5> b{6,7,8,9,10};

for(auto [x,y] : zip(a,b)) {
    std::cout << x << ", " << y << std::endl;
}

Will produce the following output

1, 6
2, 7
3, 8
4, 9
5, 10

Containers of different size

For containers with different sizes, the smallest container determines the length of of the zip iteration.

std::array<int, 4> d{1,2,3,4};
std::array<int, 2> e{5,6};

for(auto [x,y] : zip(d,e)) {
    std::cout << x << ", " << y << std::endl;
}

Will produce the following output

1, 5
2, 6

Specifically, two zip iterators are equal (operator!= is false) as soon as at least one of the individual iterators are equal.

Higher iterator acategories

If the containers support it, it is possible to use higher iterator categories' functions. For example, the iterator::operator[] on two std::arrays:

std::array<int, 2> d{1,2};
std::array<int, 2> e{3,4};

auto zipped = zip(d, e);
// only works with random access iterators
std::cout << std::get<0>(zipped.begin()[1]) << std::endl; // outputs 2 (which is the second element in the first container.)

Iterator traits for zip iterators

The zip iterator category depends on the given input containers' iterators. To achieve that, the iterzip namespace provides a natural extension of std::iterator_traits, called iterzip::iterator_traits. The chosen iterator category is always the lowest category of all input iterator types.

using T1 = std::list<int>::iterator;
using T2 = std::array<int>::iterator;
using cat = typename iterzip::iterator_traits<T1,T2>::iterator_category;
// cat == std::bidirectional_iterator_tag;

The zipped value_type is a std::tuple<X, ...> where the X are the individual iterators' value_type. The reference typedef is std::tuple<X&, ...> and pointer is mapped to reference*.

Compiling / Building / Including

In your project, simply include the header file iterzip.hpp and make sure you have support for C++17.

To build the example file provided in the repository, run

$ gcc main.cpp -o main -lstdc++ -std=c++17
$ ./main

The implementation of iterzip uses fold expressions, which are only available after C++17.