C# anonymous object as parameter not working

Question

https://dotnetfiddle.net/446j0U link to reproduce (failed on .net 4.7.2 not on .net core)


public class TEST { 

   static public void Main(string[] args)
    {
        var test = new { Text = "test", Slab = "slab"};
        Console.WriteLine(test.Text); //outputs test
        Console.WriteLine(TEST.TestMethod(test));  //outputs slab
    }

    static public string TestMethod(dynamic obj)
    {
        return obj.Slab;
    }
}

access to anonymous object in the same function is working OK but when I try to pass it in the function I'm getting exception

Run-time exception (line 14): Attempt by method 'DynamicClass.CallSite.Target(System.Runtime.CompilerServices.Closure, System.Runtime.CompilerServices.CallSite, System.Object)' to access type '<>f__AnonymousType0`2' failed.

Stack Trace:

[System.TypeAccessException: Attempt by method 'DynamicClass.CallSite.Target(System.Runtime.CompilerServices.Closure, System.Runtime.CompilerServices.CallSite, System.Object)' to access type '<>f__AnonymousType0`2' failed.] at CallSite.Target(Closure , CallSite , Object ) at System.Dynamic.UpdateDelegates.UpdateAndExecute1[T0,TRet](CallSite site, T0 arg0) at TEST.TestMethod(Object obj) :line 14 at TEST.Main(String[] args) :line 9

Edit by @RandRandom:

Since the bounty period is almost over, I decided to edit this question.

The given answers so far all fail to actually answer the problem at hand and only give ways to avoid the error.

OP clearly stated (in comments) that he is aware of workarounds and is currently using a workaround.

Those questions still remain

WHY is the mentioned error occuring on OPs setup and on dotnetfiddle.net?
If the error got fixed with an update what would OP need to update?
Got the problem fixed in a new compiler / .Net Version / Visual Studio version?

To recap here are OP's Information so far:

VS 2017
.Net Framework 4.8

Doing this is likely a very bad idea. That said, your code is working fine in both LinqPad 5 and 6, so I am unable to replicate. Anything special with your project setup? — Jonathon Chase
– Jonathon Chase, Commented Nov 19, 2019 at 15:42
Rand is rigth, no repro dotnetfiddle.net/usRSXU in .net core 3 but repro in 4.7.2 dotnetfiddle.net/PwtQxy . @RandRandom What framework did you try it on ? — xdtTransform
– xdtTransform, Commented Nov 19, 2019 at 15:45
Just as a curious note, If you add newtonsoft to the nuget packages, but without altering the code, it works. dotnetfiddle.net/2Mm9Ln I think this problem is related to dotnetfiddle. — Luis Lavieri
– Luis Lavieri, Commented Nov 19, 2019 at 16:34
It works for me even in VS2017 + 4.6.1. If it ever was a bug, it's fixed now, so why the bounty? — Simon Mourier
– Simon Mourier, Commented Nov 23, 2019 at 10:03

Badri · Accepted Answer · 2019-11-25 13:56:22Z

7

As C# documentation says:

Anonymous types provide a convenient way to encapsulate a set of read-only properties into a single object without having to explicitly define a type first. The type name is generated by the compiler and is not available at the source code level. The type of each property is inferred by the compiler.

There are two obvious ways:

1) Replace anonymous type with pre-defined:

    public class Container {
        public string Test { get; set; }
        public string Slab { get; set; }
    }

    public static void Main(string[] args) {
        var test = new Container { Text = "test", Slab = "slab"};
        Console.WriteLine(test.Text); //outputs test
        Console.WriteLine(TestMethod(test));  //outputs slab
    }

    public static string TestMethod(dynamic obj) {
        return obj.Slab;
    }

This way restricts you not to use an anonymous type. But it will work fine.

2) or if you like anonymous types, use casting with ExpandoObject.

Documentation: https://learn.microsoft.com/en-us/dotnet/api/system.dynamic.expandoobject?redirectedfrom=MSDN&view=netframework-4.8

Sample: https://sebnilsson.com/blog/convert-c-anonymous-or-any-types-into-dynamic-expandoobject/

edited Nov 25, 2019 at 13:56

Badri

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answered Nov 20, 2019 at 8:14

Egor Samets

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1 Comment

user3038144 Over a year ago

Thank you Egor. I can't mark it as answer because it should work the way I'm using it (at least I need clear explanation from MS why it works in .net core). But it's the workaround I'm using.

Berkay Yaylacı · Accepted Answer · 2019-11-27 11:51:15Z

2

+25

This should work,

static public string TestMethod(dynamic obj) {
     return obj.GetType().GetProperty("Slab").GetValue(obj).ToString();
}

answered Nov 27, 2019 at 11:51

Berkay Yaylacı

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Comments

GDI89 · Accepted Answer · 2019-11-27 14:17:50Z

0

You can use ExpandoObject for dynamic type of variables or dynamic parameters. https://learn.microsoft.com/en-us/dotnet/api/system.dynamic.expandoobject?redirectedfrom=MSDN&view=netframework-4.8

public class TEST { 

   static public void Main(string[] args)
    {
        dynamic test = new ExpandoObject();
        test.Text = "test";
        test.Slab = "slab";
        Console.WriteLine(test.Text);
        Console.WriteLine(TEST.TestMethod(test));
    }

    static public string TestMethod(dynamic obj)
    {
        return obj.Slab;
    }
}

edited Nov 27, 2019 at 14:17

answered Nov 25, 2019 at 13:37

GDI89

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Comments

Kai Hartmann · Accepted Answer · 2019-11-29 14:17:30Z

0

This is a problem with .NET Fiddle. The code is working perfectly fine with the latest Visual Studio 2017 update (15.9.17) and .NET 4.7.2.

answered Nov 29, 2019 at 14:17

Kai Hartmann

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Comments

pensum · Accepted Answer · 2019-11-23 15:31:40Z

-1

This is an issue with .Net framework. You have to use Datatype which already exist and use var. Alternate way to code this is to use dictionary.

demo

using System; 
using System.Collections.Generic;

public class TEST 
{ 
   static public void Main(string[] args)
    {
        var test =  new Dictionary<int, string>();
        test.Add(1,"One");
        Console.WriteLine(test); //outputs test
        Console.WriteLine(TEST.TestMethod(test));  //outputs slab
    }

    static public string TestMethod(dynamic obj)
    {
        foreach (KeyValuePair<int, string> item in obj)
        {
            Console.WriteLine("Key: {0}, Value: {1}", item.Key, item.Value);
            return item.Value;
        }
        return "";   
    }
}

edited Nov 23, 2019 at 15:31

pensum

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answered Nov 22, 2019 at 18:39

Jin Thakur

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