3

There are similar questions to this - but so far none of them helped.

I'm calling:

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

Then in a section of my code, VS is pointing out errors in the LINQ methods (.Last() and .Max() ). I hovered over the .Max(). The error says:

The call is ambiguous between the following methods or properties: 'System.Linq.Enumerable.Max(System.Collections.Generic.IEnumerable<int>)' and 'System.Linq.Enumerable.Max(System.Collections.Generic.IEnumerable<int>)'

I've tried re-installing all of my references and packages, I restarted VS, IIS (this is a website). VS recognizes System.Linq so that's not an issue....

I can't figure out why this is all the sudden throwing errors.

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bagofmilk
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  • It seems you somehow have two distinct `System.Linq.Enumerable` candidates. – InBetween Jan 04 '19 at 20:50
  • How is this possible? I thought VS prevents you from adding identical references – bagofmilk Jan 04 '19 at 20:52
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    It doesn't have to be identical references. Someone being oversmart and implementing a `System.Linq.Enumerable` is enough. – InBetween Jan 04 '19 at 21:02
  • How should I go about finding this additional reference? – bagofmilk Jan 04 '19 at 21:07
  • You can try to [reference the System.Linq namespace from a specific assembly](https://stackoverflow.com/questions/517058/how-to-reference-a-namespace-from-a-specific-assembly) to see if that resolves the issue. – John Wu Jan 04 '19 at 21:35
  • Comment out `using System.Collections.Generic;`. Then `Go to definition` / `Go to implementation` on the `Max` call - where does it take you? – mjwills Jan 04 '19 at 22:09

1 Answers1

4

This can happen if anywhere in your code or in a referenced assemby someone has had the horrible horrible idea of implementing their own IEnumerable<T> extension methods and not knowing better, used the same namespace as the ones provided by the framework:

  • Alpha assembly rolls their own IEnumerable<T> extension methods in System.Linq namespace:

    namespace System.Linq {
    public static class MyEnumerable {
        public static T Max<T>(this IEnumerable<T> source) { //...
        }
    //... 
    }
}

  • Assembly Charlie thinks Alpha is great due to some other functionality it provides and references it completely oblivious to the nasty surprise it hides inside.

    using System.Linq; //woops

namespace Charlie {
    class C {
        void Foo() {
            var l = new List<object>() { 1, 2, 3 };
            var m = l.Max() /*compile time error. Ambiguous call*/ } }
}

I don't know if this can be your case but its a probable scenario. Another potential candidate could be some versioning conflict but I'm not really sure if that is even possible in VS. I've never run into anything similar with System.* namespaces.

InBetween
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  • ahhh f***.... I just did a find all of System.Linq and currently nothing sticks out, but I think you are on to something. – bagofmilk Jan 04 '19 at 21:18