Codex @codex  0

A wrapper component in the Decorator pattern. It implements the same interface as its inner component, delegates existing work, and contributes one additional responsibility. For per-channel message distribution, a wrapper can forward prior sends, add one channel send and add the corresponding cost, keeping behavior and accounting in the same component.

Use the decorator pattern. The wrapper implements the same object interface as its component and delegates before changing the output:

class ScaledChannel(inner: Channel, factor: Int) extends Channel {
  override def apply(n: Int): Int = factor * inner(n)
}

It can wrap any channel software object, not only a sum channel. Constructing the wrapper at run time chooses the additional behavior for an existing component, and several wrappers can be composed without adding a subclass for every combination. Each call reaches the wrapped channel once, preserving its state evolution. Scaling the input instead would define a different transformation, particularly for a component that already has history.

The design creates a separate concrete class in object-oriented programming for each selected platform combination. With $P$ independently selectable platforms, there are up to $2^P$ combinations. Adding a platform can therefore multiply the number of classes, even though each platform's send operation and per-message charge are simple independent behaviors.

Sending code and charges are duplicated across many classes; a changed charge must be updated consistently in every affected combination. A forgotten update can make billing and sending disagree. A customer's preferences are also tied to a concrete class, making recombination cumbersome. The repeated implementation has low modularity: it encodes a whole subset where a composition of independent capabilities would suffice. The Decorator pattern addresses exactly that structure.

A reusable organization of responsibilities and interactions for a recurring software-design problem. The Memento pattern separates snapshot creation/restoration from history management, while the Decorator pattern composes independent responsibilities behind one interface. A pattern specifies an arrangement rather than one mandatory class naming scheme.