Returns the index of the current value's type in the SumType's
Types.
Note that Types does not include type qualifiers that are
applied to the SumType itself. To obtain the properly-qualified type
of a qualified SumType's value, use std.traits.CopyTypeQualifiers.
Returns the index of the current value's type in the SumType's Types.
Note that Types does not include type qualifiers that are applied to the SumType itself. To obtain the properly-qualified type of a qualified SumType's value, use std.traits.CopyTypeQualifiers.