Command

Encapsulates a request as an object, allowing parameterization, queuing, logging, and undo operations.

Context

You need to implement undo/redo, queue tasks, execute offline, or audit user actions.

Problem

A direct method cannot be reversed, logged, or queued.

Solution

Each action becomes an ICommand object with Execute() and optionally Undo().

#Example in C#

public interface ICommand { void Execute(); void Undo(); }

public class AddTextCommand : ICommand
{
    private readonly Document _doc; private readonly string _text;
    public AddTextCommand(Document d, string t) { _doc = d; _text = t; }
    public void Execute() => _doc.Append(_text);
    public void Undo()    => _doc.RemoveLast(_text.Length);
}

public class CommandHistory
{
    private readonly Stack<ICommand> _stack = new();
    public void Run(ICommand c) { c.Execute(); _stack.Push(c); }
    public void Undo()          { if (_stack.TryPop(out var c)) c.Undo(); }
}

When NOT to use it

When you don't need undo/queue/log: adds boilerplate without value.

Tradeoffs

Pro	Con
Enables undo, queue, audit, replay	One class per action
Decouples sender and receiver	More memory if history is stored

#behavioral #gof #undo