LA0113: Method Interception Aspect Applied to an Instance Constructor


Severity	Error
Reported by	PostSharp
Message	`Cannot apply the aspect "<Aspect>" to the instance constructor of type "<Type>": a method interception aspect cannot be applied to an instance constructor. Restrict the aspect to methods, for example with the AttributeTargetElements property.`

Cause

A MethodInterceptionAspect replaces the body of its target method with a call to OnInvoke, which decides whether to proceed to the original method. PostSharp does not support this transformation on constructors: it reports LA0113 instead of weaving the aspect into an instance constructor.

The usual cause is multicasting: when you apply the aspect to a class, PostSharp applies it to the members that the aspect accepts, and MethodInterceptionAspect accepts both methods and instance constructors. PostSharp also reports LA0113 when an IAspectProvider provides the aspect to a constructor, or when an OnMethodInvokeAdvice targets a constructor.

<Type> is the type that declares the constructor. When the aspect is multicast from a class, the message points to the class.

In the following example, the [Log] aspect is applied to the OrderService class, so it is also applied to its constructor.

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using System;
using PostSharp.Aspects;
using PostSharp.Serialization;

namespace Errors.LA0113_Error;

[PSerializable]
public class LogAttribute : MethodInterceptionAspect
{
    public override void OnInvoke( MethodInterceptionArgs args )
    {
        Console.WriteLine( $"Calling {args.Method.Name}." );
        args.Proceed();
    }
}

// The aspect is multicast to all methods of the class, including its constructor.
[Log]
public class OrderService
{
    private readonly string _warehouse;

    public OrderService( string warehouse )
    {
        this._warehouse = warehouse;
    }

    public void PlaceOrder( string product ) => Console.WriteLine( $"Order for {product} placed in {this._warehouse}." );
}

public static class Program
{
    public static void Main()
    {
        new OrderService( "Brussels" ).PlaceOrder( "Chair" );
    }
}

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error LA0113: LA0113_Error.cs(19,14): Cannot apply the aspect "Errors.LA0113_Error.LogAttribute" to the instance constructor of type "Errors.LA0113_Error.OrderService": a method interception aspect cannot be applied to an instance constructor. Restrict the aspect to methods, for example with the AttributeTargetElements property.

Resolution

Restrict the aspect to methods:

Set the AttributeTargetElements property of the aspect to Method where you apply it to a class.
When an IAspectProvider provides the aspect, skip the constructors in its ProvideAspects method.

In the following example, the aspect applies to the PlaceOrder method only.

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using System;
using PostSharp.Aspects;
using PostSharp.Extensibility;
using PostSharp.Serialization;

namespace Errors.LA0113_Fixed;

[PSerializable]
public class LogAttribute : MethodInterceptionAspect
{
    public override void OnInvoke( MethodInterceptionArgs args )
    {
        Console.WriteLine( $"Calling {args.Method.Name}." );
        args.Proceed();
    }
}

// The aspect is multicast to the methods of the class only.
[Log( AttributeTargetElements = MulticastTargets.Method )]
public class OrderService
{
    private readonly string _warehouse;

    public OrderService( string warehouse )
    {
        this._warehouse = warehouse;
    }

    public void PlaceOrder( string product ) => Console.WriteLine( $"Order for {product} placed in {this._warehouse}." );
}

public static class Program
{
    public static void Main()
    {
        new OrderService( "Brussels" ).PlaceOrder( "Chair" );
    }
}

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Calling PlaceOrder.
Order for Chair placed in Brussels.

Cause

Resolution

See Also