Add Dart_ListGetRange

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 6536e08d26540ffeb475b6a4e8127a3b38d596e7..137d9a54f68c4d7ce1a3f40f6dc0b91a65ac6b04 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -2734,6 +2734,51 @@ DART_EXPORT Dart_Handle Dart_ListGetAt(Dart_Handle list, intptr_t index) {
 }
 
 
+#define GET_LIST_RANGE(isolate, type, obj, offset, length)                     \
+  const type& array_obj = type::Cast(obj);                                     \
+  if ((offset >= 0) && (offset + length < array_obj.Length())) {               \
+    for (intptr_t index = 0; index < length; ++index)                          \
+      result[index] = Api::NewHandle(isolate, array_obj.At(index + offset));   \

[siva, 2015/08/12 17:07:25]

We normally use { ... } even if there is only one statement in the block.

+    return Api::Success();                                                     \
+  }                                                                            \
+  return Api::NewError("Invalid index passed in to access list element");      \

[siva, 2015/08/12 17:07:25]

Invalid offset/index passed.....

+
+
+DART_EXPORT Dart_Handle Dart_ListGetRange(Dart_Handle list,
+                                          intptr_t offset,
+                                          intptr_t length,
+                                          Dart_Handle* result) {
+  Isolate* isolate = Isolate::Current();
+  DARTSCOPE(isolate);

[siva, 2015/08/12 17:07:25]

if (result == NULL) {
  RETURN_NULL_ERROR(result);
}

+  const Object& obj = Object::Handle(isolate, Api::UnwrapHandle(list));
+  if (obj.IsArray()) {
+    GET_LIST_RANGE(isolate, Array, obj, offset, length);
+  } else if (obj.IsGrowableObjectArray()) {
+    GET_LIST_RANGE(isolate, GrowableObjectArray, obj, offset, length);
+  } else if (obj.IsError()) {
+    return list;
+  } else {
+    CHECK_CALLBACK_STATE(isolate);
+    // Check and handle a dart object that implements the List interface.
+    const Instance& instance =
+        Instance::Handle(isolate, GetListInstance(isolate, obj));
+    if (!instance.IsNull()) {
+      for (intptr_t index = 0; index < length; ++index) {
+        Dart_Handle value = Api::NewHandle(isolate, Send1Arg(
+          instance,
+          Symbols::IndexToken(),
+          Instance::Handle(isolate, Integer::New(index))));

[siva, 2015/08/12 17:07:25]

This would be a little more optimal if we did not use Send1Arg in the loop.
Send1Arg resolves the function '[]' and we could hoist that out of the loop.

Something like:
  const intptr_t kNumArgs = 2;
  ArgumentsDescriptor args_desc(
      Array::Handle(ArgumentsDescriptor::New(kNumArgs)));
  const Function& function = Function::Handle(
      Resolver::ResolveDynamic(receiver, selector, args_desc));
  if (function.IsNull()) {
    return ApiError::New(String::Handle(String::New("")));
  }
  const Array& args = Array::Handle(Array::New(kNumArgs));
  args.SetAt(0, receiver);
  Instance& index = Instance::Handle(isolate);
  for (intptr_t index = 0; index < length; ++index) {
    index = Integer::New(index);
    args.SetAt(1, index);
    Dart_Handle value =
        Api::NewHandle(isolate,
                       DartEntry::InvokeFunction(function, args));
    ...
    ...
  }

+        if (Dart_IsError(value))
+          return value;
+        result[index] = value;
+      }
+      return Api::Success();
+    }
+    return Api::NewError("Object does not implement the 'List' interface");
+  }
+}
+
+
 #define SET_LIST_ELEMENT(isolate, type, obj, index, value)                     \
   const type& array = type::Cast(obj);                                         \
   const Object& value_obj = Object::Handle(isolate, Api::UnwrapHandle(value)); \