Add dll_iterator

src/util/dlist.h

@@ -17,9 +17,11 @@ Revision History:
 
 --*/
 #pragma once
+#include <type_traits>
 
+template <typename T> class dll_iterator;
 
-template<typename T>
+template <typename T>
 class dll_base {
     T* m_next { nullptr };
     T* m_prev { nullptr };
@@ -27,6 +29,8 @@ public:
 
     T* prev() { return m_prev; }
     T* next() { return m_next; }
+    T const* prev() const { return m_prev; }
+    T const* next() const { return m_next; }
 
     void init(T* t) {
         m_next = t;
@@ -105,11 +109,10 @@ public:
         return true;
     }
 
-
-    static bool contains(T* list, T* elem) {
+    static bool contains(T const* list, T const* elem) {
         if (!list)
             return false;
-        T* first = list;
+        T const* first = list;
         do {
             if (list == elem)
                 return true;
@@ -120,5 +123,59 @@ public:
     }
 };
 
+template <typename T>
+class dll_iterator {
+    T const* m_elem;
+    bool m_first;
 
+    dll_iterator(T const* elem, bool first): m_elem(elem), m_first(first) { }
 
+public:
+    static dll_iterator mk_begin(T const* elem) {
+        // Setting first==(bool)elem makes this also work for elem==nullptr;
+        // but we can't implement top-level begin/end for pointers because it clashes with the definition for arrays.
+        return {elem, (bool)elem};
+    }
+
+    static dll_iterator mk_end(T const* elem) {
+        return {elem, false};
+    }
+
+    // using value_type = T;
+    // using pointer = T const*;
+    // using reference = T const&;
+    // using iterator_category = std::input_iterator_tag;
+
+    dll_iterator& operator++() {
+        m_elem = m_elem->next();
+        m_first = false;
+        return *this;
+    }
+
+    T const& operator*() const {
+        return *m_elem;
+    }
+
+    bool operator==(dll_iterator const& other) const {
+        return m_elem == other.m_elem && m_first == other.m_first;
+    }
+
+    bool operator!=(dll_iterator const& other) const {
+        return !operator==(other);
+    }
+};
+
+template < typename T
+         , typename U = std::enable_if_t<std::is_base_of_v<dll_base<T>, T>>  // should only match if T actually inherits from dll_base<T>
+         >
+dll_iterator<T> begin(T const& elem) {
+    return dll_iterator<T>::mk_begin(&elem);
+}
+
+template < typename T
+         , typename U = std::enable_if_t<std::is_base_of_v<dll_base<T>, T>>  // should only match if T actually inherits from dll_base<T>
+         >
+dll_iterator<T> end(T const& elem)
+{
+    return dll_iterator<T>::mk_end(&elem);
+}