Facade

Provide a unified interface to a set of interfaces in a subsystem, defining a higher-level interface that makes the subsystem easier to use. Use it when you want to provide a simple interface to a complex subsystem, when there are many dependencies between clients and implementation classes, or when you want to layer your subsystems with a defined entry point.

Examples:

• When you call a shop to place an order by phone, the operator is your facade — one simple voice interface that routes your request to the ordering system, payment gateway, and delivery service behind the scenes. In code, a VideoConversionFacade exposes a single encode(filename, format) method that internally orchestrates dozens of video-library objects.

// Facade unifies a compiler subsystem behind one class
class Compiler {
public:
  Compiler();
  virtual void Compile(istream& input, BytecodeStream& output) {
    Scanner scanner(input);
    ProgramNodeBuilder builder;
    Parser parser;
    parser.Parse(scanner, builder);
    RISCCodeGenerator generator(output);
    ProgramNode* parseTree = builder.GetRootNode();
    parseTree->Traverse(generator);
  }
};