Question SystemAPI.Query's question.

Thank you for read my post

in the ECS 1.0 doc,
(https://docs.unity3d.com/Packages/com.unity.entities@1.0/manual/systems-systemapi-query.html)

Doc said that "However, because it only reads the RotationSpeed data, it uses RefRO<T>. RefRO<T> usage is entirely optional: you could use the following instead as valid code"

Optional mean that syntex is totally same as RefRO<T> == Data <T>
or
RefRO<T> will have safety check, Data<T> will not have safety check?

Just confuse to use the syntext. Anyone know about it?

Thank you.

 

They're the same in that you can't write to either but they're not syntactically the same.

RefRO gives you a reference to the data and without RefRO you get a copy of the data.
The reason you would use RefRO is for performance in that it avoids copying all your data.
If your components are small (8 bytes) or performance is of no concern, then you can leave off RefRO and avoid the syntax overhead.

The safety check that RefRO performs on ValueRO access is part of the job safety system and in the given scenario, you're safe whether you use RefRO or not.

 

First, Thank you for reply.

Ah ha! performance! Thank you.
And, also, I didn't know that reading will cause copy. Thank you for let me know that too.