Interface-implementing anonymous class in C#?

Question

Is there a construct in C# which allows you to create a anonymous class implementing an interface, just like in Java?

related http://stackoverflow.com/questions/191013/can-a-c-sharp-anonymous-class-implement-an-interface — mcabral, Mar 22 '12 at 14:39
You're confusing lambda expressions (anonymous functions) with anonymous classes. It makes no sense for a function to implement interfaces — dtech, Mar 22 '12 at 14:40

Servy · Accepted Answer · 2014-06-23T16:53:40.960

32

As has already been stated, no, this is not possible. However, you can make a class that implements the desired interface and accepts a lambda in it's constructor so that you can turn a lambda into a class that implements the interface. Example:

public class LambdaComparer<T> : IEqualityComparer<T>
{
    private readonly Func<T, T, bool> _lambdaComparer;
    private readonly Func<T, int> _lambdaHash;

    public LambdaComparer(Func<T, T, bool> lambdaComparer) :
        this(lambdaComparer, EqualityComparer<T>.Default.GetHashCode)
    {
    }

    public LambdaComparer(Func<T, T, bool> lambdaComparer,
        Func<T, int> lambdaHash)
    {
        if (lambdaComparer == null)
            throw new ArgumentNullException("lambdaComparer");
        if (lambdaHash == null)
            throw new ArgumentNullException("lambdaHash");

        _lambdaComparer = lambdaComparer;
        _lambdaHash = lambdaHash;
    }

    public bool Equals(T x, T y)
    {
        return _lambdaComparer(x, y);
    }

    public int GetHashCode(T obj)
    {
        return _lambdaHash(obj);
    }
}

Usage (obviously doing nothing helpful, but you get the idea)

var list = new List<string>() { "a", "c", "a", "F", "A" };
list.Distinct(new LambdaComparer<string>((a,b) => a == b));

edited Jun 23 '14 at 16:53

answered Mar 22 '12 at 16:12

Servy

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2

Ooh, a little bit fancy! – Michael Rodrigues Aug 29 '12 at 02:30
2

this is the best solution for this problem i have seen yet, genius – Willem D'Haeseleer Nov 22 '12 at 09:42
1

very cool solution. The main drawback is you have to create a base class for every interface. Is there any simple way to make it generic? – Louis Rhys Apr 16 '13 at 03:29
1

@LouisRhys Simple, no. You'd need to create the new concrete type at compile time by emitting the IL code for it directly. It would be be fairly difficult to do. – Servy Apr 17 '13 at 13:36
+1. Similar to solution here http://stackoverflow.com/a/8941871/661933 – nawfal Apr 19 '13 at 18:25
1

@nawfal Yeah, the pattern has been floating around for a while. I've seen it used a number of times in various places. – Servy Apr 19 '13 at 18:29

score 6 · Answer 2 · answered Mar 22 '12 at 14:37

6

No. C# doesn't support anonymous classes (except anonymous types which can't define methods).

answered Mar 22 '12 at 14:37

oxilumin

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score 2 · Answer 3 · answered Mar 22 '12 at 14:38

2

No, a Lambda Expression can not implement any additional interfaces than it already does.

You're also comparing the wrong things. I'm guessing you really meant to ask if anonymous types in C# can implement interfaces. The answer to that is also no.

answered Mar 22 '12 at 14:38

Justin Niessner

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Interface-implementing anonymous class in C#?

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