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child-aspects.md

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The document explains how to add child aspects in Metalama Framework, the conditions they must follow, and how to access the parent aspect.

Adding child aspects

An aspect can introduce other aspects to child declarations. These aspects are known as child aspects. Child aspects must adhere to two conditions:

  • The child aspect class should be processed after the parent aspect class. In other words, the child aspect class must be listed before the parent class in the xref:Metalama.Framework.Aspects.AspectOrderAttribute ordering definition. Please refer to xref:ordering-aspects for more details.
  • The target declaration of the child aspect class must be included in the target type of the parent aspect. For example, a type-level aspect can introduce aspects to methods of the current type, but not to methods of a different type. A parameter-level aspect can add a child aspect to the parent method or another method of the same type, but not of a different type.

An aspect can add child aspects from the xref:Metalama.Framework.Aspects.IAspect`1.BuildAspect* method by using the xref:Metalama.Framework.Aspects.IAspectBuilder`1.Outbound?text=builder.Outbound property, followed by calling the xref:Metalama.Framework.Aspects.IAspectReceiver`1.AddAspect* method. To introduce child aspects on members of the current declaration, use the xref:Metalama.Framework.Aspects.IAspectReceiver`1.Select* or xref:Metalama.Framework.Aspects.IAspectReceiver`1.SelectMany* method, and then invoke xref:Metalama.Framework.Aspects.IAspectReceiver`1.AddAspect*.

Accessing the parent aspect

Parent aspects are enumerated in the xref:Metalama.Framework.Aspects.IAspectPredecessor.Predecessors?text=IAspectPredecessor.Predecessors property. The child aspect can access this from xref:Metalama.Framework.Aspects.meta.AspectInstance?text=meta.AspectInstance or xref:Metalama.Framework.Aspects.IAspectBuilder.AspectInstance?text=builder.AspectInstance.