NBMsgPack011: [DerivedTypeShape] alias must be unique

DerivedTypeShapeAttribute should specify an alias that is unique within the scope of the type it is applied to.

Learn more about subtype unions.

Example violations

[DerivedTypeShape(typeof(DerivedType1), Tag = 1)]
[DerivedTypeShape(typeof(DerivedType2), Tag = 1)] // Reused an alias
class BaseType
{
}

class DerivedType1 : BaseType
{
}

class DerivedType2 : BaseType
{
}

Resolution

Change the alias to one that has not yet been used.

[DerivedTypeShape(typeof(DerivedType1), Tag = 1)]
[DerivedTypeShape(typeof(DerivedType2), Tag = 2)]
class BaseType
{
}

class DerivedType1 : BaseType
{
}

class DerivedType2 : BaseType
{
}

Additional examples

Note that across types, the alias does not need to be unique. The following is perfectly valid:

[DerivedTypeShape(typeof(DerivedFromBaseType), Tag = 1)]
class BaseType
{
}

[DerivedTypeShape(typeof(DerivedFromAnotherType), Tag = 1)]
class AnotherType
{
}