Mojo: more idiomatic C++ bindings

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

-{%- set class_name = struct.name -%}
-{%- set dtor_name = [] %}
-{%- if struct|is_struct_with_handles %}
-{%-   set _ = dtor_name.append("&internal::%s_Data_Destructor"|format(struct.name)) %}
-{%- else %}
-{%-   set _ = dtor_name.append("NULL") %}
-{%- endif %}
-
-{%- macro set_default(kind, value, depth) -%}
-{#--- Strings ---#}
-{%-   if kind|is_string_kind -%}
-{{caller("mojo::String(" ~ value|expression_to_text(module) ~ ")")}}
-{#--- Arrays ---#}
-{%-   elif kind|is_array_kind %}
-{%-     set _ = value|verify_token_type("ARRAY") %}
-{
-  {{kind|cpp_wrapper_type}}::Builder tmp{{depth}}({{value[1]|length}});
-{%-     for element in value[1] %}
-{%-       filter indent(2) %}
-{%-         call(result) set_default(kind.kind, element, depth+1) %}
-tmp{{depth}}[{{loop.index0}}] = {{result}};
-{%-         endcall %}
-{%-       endfilter %}
-{%-     endfor -%}
-  {{caller("tmp" ~ depth ~ ".Finish()")|indent(2)}}
-}
-{#--- Objects ---#}
-{%-   elif kind|is_object_kind %}
-{%-     set _ = value|verify_token_type("OBJECT") %}
-{
-  {{kind|cpp_wrapper_type}}::Builder tmp{{depth}};
-{%-   set struct = kinds[kind.spec] %}
-{%-   for element in value[1] %}
-{#-     Use struct.packed_fields to order struct values by ordinal number #}
-{%-     set subfield = struct.fields[loop.index0] %}
-{%-     filter indent(2) %}
-{%-       call(result) set_default(subfield.kind, element, depth+1) %}
-tmp{{depth}}.set_{{subfield.name}}({{result}});
-{%-       endcall %}
-{%-     endfilter %}
-{%-   endfor -%}
-  {{caller("tmp" ~ depth ~ ".Finish()")|indent(2)}}
-}
-{#--- POD types ---#}
-{%-   else -%}
-{{caller(value|expression_to_text(module))}}
-{%-   endif %}
-{%- endmacro %}
-
-{{class_name}}::Builder::Builder(mojo::Buffer* buf)
-    : data_(Data::New(buf, {{dtor_name[0]}})) {
-{%- for pf in struct.packed.packed_fields if pf.field.default %}
-{%-   filter indent(2) %}
-{%-     call(result) set_default(pf.field.kind, pf.field.default, 0) %}
-set_{{pf.field.name}}({{result}});
-{%-     endcall %}
-{%-   endfilter %}
-{%- endfor %}
-}
-
-{{class_name}} {{class_name}}::Builder::Finish() {
-  Data* data = NULL;
-  std::swap(data, data_);
-  return mojo::internal::Wrap(data);
-}