Allow comparing arrays with different element types.

c++/src/kj/common-test.c++

@@ -471,6 +471,27 @@ TEST(Common, ArrayAsBytes) {
   }
 }
 
+KJ_TEST("ArrayPtr operator ==") {
+  KJ_EXPECT(ArrayPtr<const int>({123, 456}) == ArrayPtr<const int>({123, 456}));
+  KJ_EXPECT(!(ArrayPtr<const int>({123, 456}) != ArrayPtr<const int>({123, 456})));
+  KJ_EXPECT(ArrayPtr<const int>({123, 456}) != ArrayPtr<const int>({123, 321}));
+  KJ_EXPECT(ArrayPtr<const int>({123, 456}) != ArrayPtr<const int>({123}));
+
+  KJ_EXPECT(ArrayPtr<const int>({123, 456}) == ArrayPtr<const short>({123, 456}));
+  KJ_EXPECT(!(ArrayPtr<const int>({123, 456}) != ArrayPtr<const short>({123, 456})));
+  KJ_EXPECT(ArrayPtr<const int>({123, 456}) != ArrayPtr<const short>({123, 321}));
+  KJ_EXPECT(ArrayPtr<const int>({123, 456}) != ArrayPtr<const short>({123}));
+
+  KJ_EXPECT((ArrayPtr<const StringPtr>({"foo", "bar"}) ==
+             ArrayPtr<const char* const>({"foo", "bar"})));
+  KJ_EXPECT(!(ArrayPtr<const StringPtr>({"foo", "bar"}) !=
+             ArrayPtr<const char* const>({"foo", "bar"})));
+  KJ_EXPECT((ArrayPtr<const StringPtr>({"foo", "bar"}) !=
+             ArrayPtr<const char* const>({"foo", "baz"})));
+  KJ_EXPECT((ArrayPtr<const StringPtr>({"foo", "bar"}) !=
+             ArrayPtr<const char* const>({"foo"})));
+}
+
 KJ_TEST("kj::range()") {
   uint expected = 5;
   for (uint i: range(5, 10)) {

c++/src/kj/common.h

@@ -1331,6 +1331,17 @@ public:
   }
   inline bool operator!=(const ArrayPtr& other) const { return !(*this == other); }
 
+  template <typename U>
+  inline bool operator==(const ArrayPtr<U>& other) const {
+    if (size_ != other.size()) return false;
+    for (size_t i = 0; i < size_; i++) {
+      if (ptr[i] != other[i]) return false;
+    }
+    return true;
+  }
+  template <typename U>
+  inline bool operator!=(const ArrayPtr<U>& other) const { return !(*this == other); }
+
 private:
   T* ptr;
   size_t size_;