custom-attributes.md

Custom attributes

To use custom attributes, derive from System.Attribute and register them with the setup API:

• TagAttribute
• OrdinalAttribute
• TypeAttribute You can also use combined attributes. Each registration method can take an optional argument index (default is 0) that specifies where to read tag, ordinal, or type metadata.

using Shouldly;
using Pure.DI;

DI.Setup(nameof(PersonComposition))
    .TagAttribute<MyTagAttribute>()
    .OrdinalAttribute<MyOrdinalAttribute>()
    .TypeAttribute<MyTypeAttribute>()
    .TypeAttribute<MyGenericTypeAttribute<TT>>()
    .Arg<int>("personId")
    .Bind().To(() => new Uri("https://github.com/DevTeam/Pure.DI"))
    .Bind("NikName").To(() => "Nik")
    .Bind().To<Person>()

    // Composition root
    .Root<IPerson>("Person");

var composition = new PersonComposition(personId: 123);
var person = composition.Person;
person.ToString().ShouldBe("123 Nik https://github.com/DevTeam/Pure.DI");

[AttributeUsage(
    AttributeTargets.Constructor
    | AttributeTargets.Method |
    AttributeTargets.Property |
    AttributeTargets.Field)]
class MyOrdinalAttribute(int ordinal) : Attribute;

[AttributeUsage(
    AttributeTargets.Parameter
    | AttributeTargets.Property
    | AttributeTargets.Field)]
class MyTagAttribute(object tag) : Attribute;

[AttributeUsage(
    AttributeTargets.Parameter
    | AttributeTargets.Property
    | AttributeTargets.Field)]
class MyTypeAttribute(Type type) : Attribute;

[AttributeUsage(
    AttributeTargets.Parameter
    | AttributeTargets.Property
    | AttributeTargets.Field)]
class MyGenericTypeAttribute<T> : Attribute;

interface IPerson;

class Person([MyTag("NikName")] string name) : IPerson
{
    private object? _state;

    [MyOrdinal(1)] [MyType(typeof(int))] internal object Id = "";

    [MyOrdinal(2)]
    public void Initialize([MyGenericType<Uri>] object state) =>
        _state = state;

    public override string ToString() => $"{Id} {name} {_state}";
}

dotnet --list-sdk

dotnet new console -n Sample

dotnet add package Pure.DI
dotnet add package Shouldly

dotnet run

partial class PersonComposition
{
  private readonly int _argPersonId;

  [OrdinalAttribute(128)]
  public PersonComposition(int personId)
  {
    _argPersonId = personId;
  }

  public IPerson Person
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
      string transientString = "Nik";
      Uri transientUri = new Uri("https://github.com/DevTeam/Pure.DI");
      var transientPerson = new Person(transientString);
      transientPerson.Id = _argPersonId;
      transientPerson.Initialize(transientUri);
      return transientPerson;
    }
  }
}

Class diagram:

---
 config:
  class:
   hideEmptyMembersBox: true
---
classDiagram
	Uri --|> IEquatableᐸUriᐳ
	Uri --|> IFormattable
	Uri --|> ISpanFormattable
	Uri --|> ISerializable
	Person --|> IPerson
	PersonComposition ..> Person : IPerson Person
	Person o-- Int32 : Argument "personId"
	Person *-- Uri : Uri
	Person *-- String : "NikName" String
	namespace Pure.DI.UsageTests.Attributes.CustomAttributesScenario {
		class IPerson {
			<<interface>>
		}
		class Person {
				<<class>>
			+Person(String name)
			~Object Id
			+Initialize(Object state) : Void
		}
		class PersonComposition {
		<<partial>>
		+IPerson Person
		}
	}
	namespace System {
		class IEquatableᐸUriᐳ {
			<<interface>>
		}
		class IFormattable {
			<<interface>>
		}
		class Int32 {
				<<struct>>
		}
		class ISpanFormattable {
			<<interface>>
		}
		class String {
				<<class>>
		}
		class Uri {
				<<class>>
		}
	}
	namespace System.Runtime.Serialization {
		class ISerializable {
			<<interface>>
		}
	}

See also:

• Custom universal attribute