Converting jarray to IEnumerable gives "does not contain a definition for Concat"-CodePudding

I've got the following code:

using System;
using System.Collections.Generic;
using System.Linq;
using Newtonsoft.Json;
                    
public class Program
{
    public static void Main()
    {
        var json = JsonConvert.DeserializeObject<dynamic>("[\"test1\", \"test2\"]");
        var list = json.ToObject<IEnumerable<string>>().Concat(new[] { "test3" });
        Console.WriteLine(string.Join(", ", list));
    }
}

I would expect the result to be "test1, test2, test3" but instead this throws an exception:

[Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: 'System.Collections.Generic.List' does not contain a definition for 'Concat'] at CallSite.Target(Closure , CallSite , Object , String[] ) at System.Dynamic.UpdateDelegates.UpdateAndExecute2[T0,T1,TRet](CallSite site, T0 arg0, T1 arg1) at Program.Main() :line 10

As far as I can tell in testing, both sides of the Concat should be a version of IEnumerable<string>.

I've gotten a successful try doing this:

using System;
using System.Collections.Generic;
using System.Linq;
using Newtonsoft.Json;
                    
public class Program
{
    public static void Main()
    {
        var json = JsonConvert.DeserializeObject<dynamic>("[\"test1\", \"test2\"]");
        var list = (json as IEnumerable<dynamic>).Select(item => (string)item).Concat(new[] { "test3" });
        Console.WriteLine(string.Join(", ", list));
    }
}

But that's a bit clunky.

What am I doing wrong? Am I missing something?

CodePudding user response：

Your code was super simple to fix. Here it is:

var json = JsonConvert.DeserializeObject<dynamic[]>("[\"test1\", \"test2\"]");
var list = json.Concat(new[] { "test3" });
Console.WriteLine(string.Join(", ", list));

You just needed to change dynamic to dynamic[].

Remember that dynamic is just compiler trickery for object-that-doesn't-throw-compiler-errors. But it isn't something that is enumerable. However, dynamic[] is.

But for that matter, object[], and even string[], works.

string[] json = JsonConvert.DeserializeObject<string[]>("[\"test1\", \"test2\"]");
IEnumerable<string> list = json.Concat(new[] { "test3" });
Console.WriteLine(string.Join(", ", list));

My advice is avoid dynamic in almost all cases. Use strong-typing instead.

CodePudding user response：

Borrowing the solution from here, I tried assigning the output of ToObject() method to a new variable with explicit type like so:

using Newtonsoft.Json;

public class Program
{
    public static void Main()
    {
        var json = JsonConvert.DeserializeObject<dynamic>("[\"test1\", \"test2\"]");
        IEnumerable<string> jsonAsEnumerable = json.ToObject<IEnumerable<string>>();
        var list = jsonAsEnumerable.Concat(new[] { "test3" });
        Console.WriteLine(string.Join(", ", list));
    }
}

It seems to do the trick.