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

{%- set mojom_type = union|get_qualified_name_for_kind %}

template <>
struct {{export_attribute}} UnionTraits<{{mojom_type}}::DataView,
                                        {{mojom_type}}Ptr> {
  static bool IsNull(const {{mojom_type}}Ptr& input) { return !input; }
  static void SetToNull({{mojom_type}}Ptr* output) { output->reset(); }

  static {{mojom_type}}::Tag GetTag(const {{mojom_type}}Ptr& input) {
    return input->which();
  }

{%- for field in union.fields %}
{%-   set maybe_const_in = "" if field.kind|contains_handles_or_interfaces else "const" %}
{%-   set maybe_const_out = "" if field.kind|contains_handles_or_interfaces or not field.kind|is_reference_kind else "const" %}
{#    We want the field accessor to be const whenever possible to allow
      structs to be used as map keys. #}
  static {{maybe_const_out}} {{field.kind|cpp_union_trait_getter_return_type}} {{field.name}}({{maybe_const_in}} {{mojom_type}}Ptr& input) {
    return input->get_{{field.name}}();
  }
{%- endfor %}

  static bool Read({{mojom_type}}::DataView input, {{mojom_type}}Ptr* output);
};