Decorator Generator

Source generator for decorator pattern boilerplate code in C#.

When implementing the decorator pattern in C#, it requires adding boilerplate code for every interface that needs to support decorators, namely the abstract class. Boilerplate is tedious to write and error-prone. This source generator solves this problem by automatically generating the abstract class. It only needs to be told which interfaces it should generate the abstract class for.

Getting Started

Installation

Add the library via NuGet to the project(s) that you want to auto-generate abstract decorator classes for:

• Either via Project > Manage NuGet Packages... / Browse / search for decorator-generator / Install
• Or by running a command in the Package Manager Console

Install-Package DecoratorGenerator

Usage

Add a Decorate attribute to the interface:

using DecoratorGenerator;

namespace SampleLibrary;

[Decorate]
public interface ICat
{
    string Meow();
}

Build the project so the abstract class is generated for the interface. The generated class will be named after the interface, but without the I prefix. In this case, since the interface is ICat the class will be CatDecorator. Then create your decorator class as usual:

namespace SampleLibrary;

public class BarkingCat : CatDecorator
{
    public BarkingCat(ICat cat) : base(cat)
    {

    }

    public override string Meow()
    {
        return $"woof woof - {base.Meow()}";
    }
}

Example usage of the decorator:

using SampleLibrary;

namespace SampleApp;

partial class Program
{

    static void Main(string[] args)
    {
        var cat = new BarkingCat(new Cat());
        var sound = cat.Meow();

        Console.WriteLine(sound);
    }

}

Configuration

List of Target Interfaces in a Config file

To generate decorator abstract classes for third party interfaces, Decorator Generator will look for a struct named WrapperList and generate classes of the types in the fields of the WrapperList:

using Amazon.DynamoDBv2.DataModel;

public struct WrapperList
{
    // name the field whatever you want, the name isn't used, only the type is used.
    IDynamoDBContext dynamoDBContext;
}

In this case, it will generate a class for IDynamoDBContext called DynamoDBContextDecorator. This feature will also work for your own interfaces if you prefer this approach instead of using the attribute.