Implement unions as members of structs.

mojo/public/tools/bindings/generators/cpp_templates/union_definition.tmpl

 {%- import "validation_macros.tmpl" as validation_macros %}
 {%- set class_name = union.name ~ "_Data" %}
 {%- set enum_name = union.name ~ "_Tag" -%}
 
 // static
 {{class_name}}* {{class_name}}::New(mojo::internal::Buffer* buf) {
   return new (buf->Allocate(sizeof({{class_name}}))) {{class_name}}();
 }
 
+

[yzshen1, 2015/02/17 19:34:35]

unnecessary empty line.

[azani, 2015/02/18 00:27:58]

Done.

 // static
 bool {{class_name}}::Validate(const void* data,
-                              mojo::internal::BoundsChecker* bounds_checker) {
+                              mojo::internal::BoundsChecker* bounds_checker,
+                              bool claim_memory) {
   if (!data) {
     return true;
   }
 
   if (!mojo::internal::IsAligned(data)) {
     ReportValidationError(mojo::internal::VALIDATION_ERROR_MISALIGNED_OBJECT);
     return false;
   }
 
-  if (!bounds_checker->ClaimMemory(data, sizeof({{class_name}}))) {
+  // If the union is inlined in another structure its memory was already claimed.

[yzshen1, 2015/02/17 19:34:35]

nit: I understand 80-char limit is not honored in general in .tmpl files, but
usually people stick to 80-char limits for comments.

[azani, 2015/02/18 00:27:57]

Done.

+  // This ONLY applies to the union itself, NOT anything which the union points to.
+  if (claim_memory && !bounds_checker->ClaimMemory(data, sizeof({{class_name}}))) {

[yzshen1, 2015/02/17 19:34:35]

For non-inlined case, we need to check that the first four bytes stores the
value 16. (I wish we could do the same for non-null inlined case, too. Please
see my comment in the declaration.)

     ReportValidationError(
         mojo::internal::VALIDATION_ERROR_ILLEGAL_MEMORY_RANGE);
     return false;
   }
   const {{class_name}}* object = static_cast<const {{class_name}}*>(data);
   MOJO_ALLOW_UNUSED_LOCAL(object);
 
   switch (object->tag) {
 {%  for field in union.fields %}
     case {{enum_name}}::{{field.name|upper}}:
@@ skipping 15 matching lines @@
 
 void {{class_name}}::EncodePointersAndHandles(
     std::vector<mojo::Handle>* handles) {
   // TODO(azani): Implement pointers and handles.
 }
 
 void {{class_name}}::DecodePointersAndHandles(
     std::vector<mojo::Handle>* handles) {
   // TODO(azani): Implement pointers and handles.
 }