Type.GetInterfaceMap with generic interface types

[pavel-agarkov]

When type parameter of Type.GetInterfaceMap method is represented by:

1. Open generic constructed type - method throws ArgumentException "interface not found" which is not mentioned in the docs
2. Closed generic constructed type - method returns InterfaceMapping with InterfaceType property equal to the specified type parameter, but not the actual version of implemented generic interface. Generic parameters in the returned type correspond to the specified type parameter, but not to the actual implemented interface type. So the following remark from the docs is incorrect:

If the current Type represents a constructed generic type, type parameters are replaced by the appropriate type arguments in the elements of the InterfaceMapping returned by this method.

dotnet core 2.1

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• ID: f037e068-f720-1ece-533e-b71e5de9b393
• Version Independent ID: 9e8ef13d-1ff6-b78e-494a-57227e2225a4
• Content: Type.GetInterfaceMap(Type) Method (System)
• Content Source: xml/System/Type.xml
• Product: dotnet-api
• GitHub Login: @dotnet-bot
• Microsoft Alias: dotnetcontent

[rpetrusha]

Thanks for pointing this out, @pavel-agarkov. We'll investigate and update the documentation accordingly in the near future.

[rpetrusha]

@pavel-agarkov, I've opened #622 to add the exception information. However, I can't reproduce your statement that

If the current Type represents a constructed generic type, type parameters are replaced by the appropriate type arguments in the elements of the InterfaceMapping returned by this method.

Do you have any code that illustrates this?

[pavel-agarkov]

@rpetrusha Exactly! This statement is from the docs - not mine. And it is incorrect.

1. The following code will throw an error: System.ArgumentException: 'Interface not found.'

typeof(List<int>).GetInterfaceMap(typeof(IList<>));

2. The following code will print Program+IHandler`1[System.Exception]
   instead of Program+IHandler`1[System.ArgumentException]

internal class Program
{
    interface IHandler<out T> where T : Exception
    {
    }

    class ArgumentHandler : IHandler<ArgumentException>
    {
    }

    static void Main(string[] args)
    {
        Console.WriteLine(
            typeof(ArgumentHandler)
            .GetInterfaceMap(typeof(IHandler<Exception>))
            .InterfaceType);
        Console.ReadKey();
    }
}

So type parameters are replaced by whatever were specified in the interfaceType and not 'appropriate type' as mentioned in the docs. This behavior made the method useless for my case.