Assignment Rules for Binding Definitions
A binding definition between two container elements is not possible if one element or expression is created with a field or structure reference and the other element or expression is created with an object reference.
Identity and compatibility of data types
Identical data types
A binding definition is possible, however, if the two container elements or expressions have identical data types. The data type is specified indirectly via the
data type reference of the relevant container element.Compatible data types
A binding definition is also possible if the two container elements or expressions have compatible data types.
Data types expressed by field references are compatible under the following circumstances:
Data types expressed by an object reference are compatible under the following circumstances:
supertype is permitted).
A binding definition from the element
However, a binding definition from an unspecified element to an element with a specified data type reference is not allowed.