JSON Schema Compiler supports functions as PropertyTypes.

tools/json_schema_compiler/cpp_type_generator.py

Index: tools/json_schema_compiler/cpp_type_generator.py
diff --git a/tools/json_schema_compiler/cpp_type_generator.py b/tools/json_schema_compiler/cpp_type_generator.py
index f398c752ec04e4348e1188e6cc89d6730a55b93b..f18b66b31d6d8675de8581fdbd7bae386a6f426b 100644
--- a/tools/json_schema_compiler/cpp_type_generator.py
+++ b/tools/json_schema_compiler/cpp_type_generator.py
@@ -152,6 +152,10 @@ class CppTypeGenerator(object):
       cpp_type = any_helper.ANY_CLASS
     elif prop.type_ == PropertyType.OBJECT:
       cpp_type = cpp_util.Classname(prop.name)
+    elif prop.type_ == PropertyType.FUNCTION:
+      # If the property is an optional function, we need to know if it whether
+      # or not it was passed.
+      cpp_type = 'bool'
     elif prop.type_ == PropertyType.ARRAY:
       item_type = prop.item_type
       if item_type.type_ == PropertyType.REF:
@@ -170,7 +174,8 @@ class CppTypeGenerator(object):
 
     # Enums aren't wrapped because C++ won't allow it. Optional enums have a
     # NONE value generated instead.

[not at google - send to devlin, 2012/07/25 01:32:33]

Add comment like "We only generate "has" methods for FUNCTIONS, so don't need to
wrap them."

[chebert, 2012/07/25 18:38:30]

Done.

-    if wrap_optional and prop.optional and prop.type_ != PropertyType.ENUM:
+    if wrap_optional and prop.optional and prop.type_ not in (PropertyType.ENUM,
+          PropertyType.FUNCTION):

[not at google - send to devlin, 2012/07/25 01:32:33]

nit: each condition on its own line, like

if (wrap_optional and
    prop.optional and
    prop.type_ not in [PropertyType.ENUM, PropertyType.FUNCTION]):

[chebert, 2012/07/25 18:38:30]

Done.

       cpp_type = 'scoped_ptr<%s> ' % cpp_type
     if pad_for_generics:
       return cpp_type