User Defined Types

When you declare a variable with a User Defined Type it can only be passed in using ByRef.
A user defined type is a value data type.
When you declare a variable with a User Defined data type it can only be passed in using ByRef.

ByRef

Passing a User Defined Type into a subroutine using ByRef allows the original variable to be changed.

ByVal

Passing a User Defined Type into a subroutine using ByVal is not possible
If you try and declare a user defined type parameter that is passed ByVal you will get a compile error.