Hapil

Hi there! Here a .NET library is being built, aimed to support and facilitate the following programming techniques for .NET developers:

• CoI - Convention over Implementation: let developers only author interfaces of application components, then let the framework dynamically generate corresponding implementations, based on conventions associated with every specific kind of the component (e.g., data transfer objects, data access layer, configuration, logging, etc etc). The conventions are authored by the users of the library. Hapil.Applied is an additional library, which supplies a set of reusable out-of-the-box conventions.
• Aspect-Oriented Programming: transparently support black-box aspects, implemented as dynamically generated CoI decorators, which intercept the calls to the components. The aspects can be connected to both hard-coded and CoI components.
• Subject-Oriented Programming: extend single inheritance in CLR with a horizontal behavior composition technique similar to traits/mixins/modules in such languages as Scala, PHP, and Ruby.
• Duck Typing: provide the Duck Typing mechanism in order to bring some of dynamic languages advantages to static programming.

Highlights

• The library is a wrapper around the .NET Reflection.Emit API. The library aims to provide a convenient, intuitive, high-level code model, which it translates into MSIL bytecode.
• The code model is exposed through type-safe and refactor-safe fluent API, which covers most of C# language constructs. Both imperative and functional programming constructs are first-class citizens in the code model.
• Implementation and decoration conventions are arranged in pipelines, so that the code generation is by itself inherently aspect-oriented.
• Second-level generics allows implementation and decoration conventions be authored as templates, yet providing the authors with type safety.
• The generated MSIL bytecode is statically bound, reflection-free, and is completely decoupled from runtime state accumulated by code generators (fine print: unless explicitly coded the other way by the authors).
• Such decoupling allows pre-compilation. This is useful when there are massive amounts of dynamic types. Instead of being generated during application initialization (or lazily later on), dynamic types can be pre-compiled and saved to an assembly, which is then loaded during application start-up, thus speeding up application initialization.
• Performance overhead introduced by aspect decorators is kept at minimum by avoiding the "Invocation Object" pattern. All aspects that apply to a component are combined together in the members of the decorator class. Moreover, when a CoI component is being decorated, the aspects are implemented inside the members of the component, with no separate decorator class.

The library also aims to:

• Provide a short and easy happy path for the discussed use cases.
• Allow writing clean and maintainable code generators, which are also type-safe and refactor-safe.
• Be lightweight, even in large applications with thousands of dynamic types.
• Make it easy to create a valid program, and make it hard to create an invalid one.
• Just work, and keep the users happy.

Now Show Me The Money!

Three - given an interface of a data transfer object:

public interface ICustomer
{
  int Id { get; set; }
  string FullName { get; set; }
  string EmailAddress { get; set; }
}

Two - plus an implementation convention:

DeriveClassFrom<object>()
  .ImplementInterface<ICustomer>()
  .AllProperties().ImplementAutomatic();

One - plus a decorator convention:

public class DataContractDecorator : ClassDecoratorBase
{
  public override void OnClassType(ClassType classType, ClassWriterBase writer)
  {
    writer.Attribute<DataContractAttribute>(values => values.Named(a => a.Namespace, "http://mydto/customer"));
  }
  public override void OnProperty(PropertyMember member, Func<PropertyDecorationBuilder> decorate)
  {
    decorate().Attribute<DataMemberAttribute>();
  }
}

GO!

[DataContract(Namespace = "http://mydto/customer")]
public sealed class CustomerDto : ICustomer
{
	private int m_Id;
	private string m_FullName;
	private string m_EmailAddress;

	[DataMember]
	public int Id
	{
		get { return this.m_Id; }
		set { this.m_Id = value; }
	}

	[DataMember]
	public string FullName
	{
		get { return this.m_FullName; }
		set { this.m_FullName = value; }
	}

	[DataMember]
	public string EmailAddress
	{
		get { return this.m_EmailAddress; }
		set { this.m_EmailAddress = value; }
	}
}

More Information

The Wiki is the ultimate source of information on the Hapil project.

Why?

For comparison of Hapil with other similar libraries, see Alternatives.

Licenses

Hapil library is developed uner the MIT License.

NUnit is licensed under zlib/libpng License (Zlib).

Moq is licensed under the New BSD License.