SequenceWrapping

public protocol SequenceWrapping : Sequence

SequenceWrapping is a type-erasing protocol that allows a Sequence-conforming structure to wrap any underlying Sequence implementation.

For example, PitchSet and PitchCollection are both containers for Pitch values, and should both be able to be used as Sequence conforming structures.

By conforming to this protocol, the PitchSet can use a Set<Pitch> as its underlying model, while PitchSequence can use an Array<Pitch> as its underlying model.

In the conforming struct, it is necessary to add a private var which is an implementation of a Sequence-conforming struct, which is then given by the sequence getter.

In the init method of the conforming struct, set the value of this private var with the given sequence.