This is also an elegant way to change the arguments to mode definition. For example I think we could singularize executor_defs, not support system_storage_defs, move logger_defs to a special resource key, etc.

I think this is a net positive. My two reservations would be:

• Two ways of doing something is worse than one.
• Operating on a function instead of a resource dict gives users an extra degree of flexibility that they might find confusing.

I don't think in this case two ways of doing things is worse. It's properly layered. Would you eliminate @solid?

Would you eliminate @solid?

I think there are almost no cases where SolidDefinition is preferable to @solid, because solids wrap functions. Unless we strongly guide them otherwise, I think some people might prefer to use ModeDefinition(resource_defs), because they might find putting their resource_defs inside a function weird.

Using SolidDefinition is desirable for framework authors. This is a layered system