Inheritance

All struct types implicitly inherit from System.ValueType, which, in turn, inherits from class object. A struct declaration may specify a list of implemented interfaces, but it is not possible for a struct declaration to specify a base class.
Struct types are never abstract and are always implicitly sealed. The abstract and sealed modifiers are therefore not permitted in a struct declaration.
Since inheritance isn't supported for structs, the declared accessibility of a struct member cannot be protected or protected internal.
Function members in a struct cannot be abstract or virtual, and the override modifier is allowed only to override methods inherited from the type System.ValueType.