Ensure a type is `Send+Sync` when `frozen_shareable` flag is used

[matsadler]

Ensure a type is `Send+Sync` when `frozen_shareable` flag is used

[matsadler]

So the constraint on DataTypeFunctions you spotted in the linked issue does it, it's just that change hasn't been released yet.

The way this works is a little convoluted.

Implementing the TypedData trait is what allows wrapping a struct. TypedData already requires Send. To implement TypedData for T you need to be able to construct a DataType. To construct a DataType you need to use DataTypeBuilder<T>, and DataTypeBuilder<T> has a bound on T that it must implement DataTypeFunctions.
The flags in the #[wrap] macro expand to calling methods on DataTypeBuilder<T> and there is an extra bound for T for the frozen_shareable method. This will error if you try to use the frozen_shareable flag for a non-Sync type.

[macournoyer]

Ah awesome! Thanks a lot.