Support Dart optional arguments which are not dispatched, but instead use default values.

client/dom/scripts/databasebuilder.py

Index: client/dom/scripts/databasebuilder.py
diff --git a/client/dom/scripts/databasebuilder.py b/client/dom/scripts/databasebuilder.py
index 81d104682d64660c57c4a72805cd71b3f7db09d3..4fd58d19cb8702f276184bf0eb71aea0155f63cb 100755
--- a/client/dom/scripts/databasebuilder.py
+++ b/client/dom/scripts/databasebuilder.py
@@ -126,13 +126,19 @@ class DatabaseBuilder(object):
     for op in interface.operations:
       for i in range(0, len(op.arguments)):
         argument = op.arguments[i]
+
+        in_optional_whitelist = (interface.id, op.id, argument.id) in optional_argument_whitelist
+        if in_optional_whitelist or set(['Optional', 'Callback']).issubset(argument.ext_attrs.keys()):
+          argument.is_optional = True
+          argument.ext_attrs['DartConvertNullToDefaultValue'] = None

[podivilov, 2012/02/28 17:46:24]

DartConvertNullToDefaultValue name doesn't reflect actual usage. Maybe
RequiredInCPP or something like that?

[antonm, 2012/02/28 19:22:08]

I am on the fence here.  To some extent this describes exactly what goes on (but
not why) and matches perfectly to conversion flags (which can be changed too, of
course).

Stephen, any thoughts?

Overall, I'd be glad to rename if you think it's a good idea---no personal
attachment to this wording :)

[sra1, 2012/02/28 22:04:42]

What is confusing to me is that 'null' and 'default value' are kind of the same
thing.  The first 'null' might be a default value or an explicit null (we can
never know).  The second 'default value' is an explicit value rather than using
the default value (not) available in C++.

Is this issue Dart specific (i.e. needs to be done this way for Frog), or native
only?  The name should reflect that.

DartiumConvertNullToExplicitDefaultValue ?
DartiumRequiresExplicitDefaultValue ?
CPPRequiresExplicitDefaultValue ?

[antonm, 2012/02/29 10:29:40]

This shouldn't be Dartium specific and should apply to JS backends as well, for
example, in those cases there is no need to do any dispatch (and you probably do
not do it anyway).

Yes, I am agree that name is somewhat confusing here and I am glad to rename it.
 Maybe reflect its semantics in our codegenerator?  Something like
DartNoDispatchOptional?  or DartDefaultValueOptional?

BTW, there is a simple trick which can allow us to provide very true optionals:

we can add _OPTIONAL = const Object(); into domimpl and make all optionals
default to it.  Now we can distinguish it from null and client code cannot pass
this fake value.

On 2012/02/28 22:04:42, sra1 wrote:

+          continue

[podivilov, 2012/02/28 17:46:24]

nit: elif

[antonm, 2012/02/28 19:22:08]

I'd prefer continue as it clearly says processing of this argument is over while
with elif one may expect some code after if.

[sra1, 2012/02/28 22:04:42]

+1 for continue

+
         if argument.is_optional:
           if 'Optional' in argument.ext_attrs:
             optional_value = argument.ext_attrs['Optional']
             if optional_value:
-              if (interface.id, op.id, argument.id) not in optional_argument_whitelist:
-                argument.is_optional = False
-                del argument.ext_attrs['Optional']
+              argument.is_optional = False
+              del argument.ext_attrs['Optional']
 
     # split operations with optional args into multiple operations
     new_ops = []