C# Language Specification

Lifted conversion operators

Given a user-defined conversion operator that converts from a non-nullable value type S to a non-nullable value type T, a lifted conversion operator exists that converts from S? to T?. This lifted conversion operator performs an unwrapping from S? to S followed by the user-defined conversion from S to T followed by a wrapping from T to T?, except that a null valued S? converts directly to a null valued T?.

A lifted conversion operator has the same implicit or explicit classification as its underlying user-defined conversion operator. The term “user-defined conversion” applies to the use of both user-defined and lifted conversion operators.

3.