feat: add iterable slice

include/utils/slice.hh

@@ -0,0 +1,52 @@
+#include <vector>
+
+namespace ppc {
+    template <class T>
+    class slice_t {
+    private:
+        T *iterable;
+        std::size_t start;
+        std::size_t n;
+    public:
+        auto begin() const { return iterable->begin() + start; }
+        auto end() const { return iterable->end() + start + n; }
+
+        auto size() const { return n; }
+        auto &operator[](std::size_t i) { return iterable[start + i]; }
+        const auto &operator[](std::size_t i) const { return iterable[start + i]; }
+
+        slice_t(T &iterable, std::size_t start, std::size_t n) {
+            this->iterable = &iterable;
+            this->start = start;
+            this->n = n;
+            if (n == -1u) this->n = iterable.size() - start;
+        }
+    };
+
+
+    template <class T>
+    inline slice_t<T> slice(slice_t<T> &sl) {
+        return slice_t<T>(sl.iterable, sl.start, sl.n);
+    }
+    template <class T>
+    inline slice_t<T> slice(slice_t<T> &sl, std::size_t start) {
+        return slice_t<T>(sl.iterable, sl.start + start, sl.n);
+    }
+    template <class T>
+    inline slice_t<T> slice(slice_t<T> &sl, std::size_t start, std::size_t n) {
+        return slice_t<T>(sl.iterable, sl.start + start, n);
+    }
+
+    template <class T>
+    inline slice_t<T> slice(T &vec) {
+        return slice_t<T>(vec, 0, vec.size());
+    }
+    template <class T>
+    inline slice_t<T> slice(T &vec, std::size_t start) {
+        return slice_t<T>(vec, start, vec.size());
+    }
+    template <class T>
+    inline slice_t<T> slice(T &vec, std::size_t start, std::size_t n) {
+        return slice_t<T>(vec, start, n);
+    }
+}