[Glacier] Add a vector iterator.

lib/glacier/container/vector.h

@@ -47,6 +47,44 @@ class Vector {
 
   T&& PopBack();
 
+  // Forward Iter
+  class Iterator {
+   public:
+    Iterator(T* item, uint64_t size) : item_(item), size_(size) {}
+
+    Iterator next() {
+      if (size_ <= 1) {
+        return {nullptr, 0};
+      }
+      return {item_ + 1, size_ - 1};
+    }
+
+    Iterator& operator++() {
+      if (size_ <= 1) {
+        item_ = nullptr;
+        size_ = 0;
+      } else {
+        item_++;
+        size_--;
+      }
+      return *this;
+    }
+
+    T& operator*() { return *item_; }
+    T* operator->() { return item_; }
+    bool operator==(const Iterator& other) { return item_ == other.item_; }
+    bool operator!=(const Iterator& other) { return item_ != other.item_; }
+
+   private:
+    T* item_;
+    uint64_t size_;
+  };
+
+  Iterator begin() { return {data_, size_}; }
+  const Iterator begin() const { return {data_, size_}; }
+  Iterator end() { return {nullptr, 0}; }
+  const Iterator end() const { return {nullptr, 0}; }
+
  private:
   T* data_;
   uint64_t size_;