Hide Delegate

Encapsulate a delegate object to reduce dependencies.

“A client is calling a method of an object of one of your fields.” – Martin Fowler

Law of Demeter support.

graph LR
    A[Client] -->|Calls| B[Server]
    B -->|Delegates| C[Delegate]

When to apply (Smells)

• Message Chains: Client calling a.getB().getC().doIt().

Motivation

• Encapsulation: The client shouldn’t need to know that B uses C to do the job.
• Low Coupling: Changes to C won’t ripple to the Client.

Mechanics (Steps)

1. Create a method on the Server class that delegates the call to the Delegate.
2. Change the client to call the Server method.

Explanation

Problem

A client calls class A, gets object B, and then calls a method on B. person.department().manager()

Solution

Create a new method in class A that delegates the call to object B. person.manager()

Real world analogy

You want to talk to the mechanics. You don’t walk into the garage; you talk to the service desk (Hide Delegate), and they talk to the mechanic.

Pros and Cons

Pros	Cons
Low coupling (Client doesn’t know Delegate)	Middle Man smell (if overused)

Comparison

• Inverse Refactoring: Remove Middle Man.

Code example

Typescript

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After

PHP

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