Why does foreach fail to find my GetEnumerator extension method?

Question

I\'m trying to make some code more readable. For Example foreach(var row in table) {...} rather than foreach(DataRow row in table.Rows) {...}.

Answer 1

This will be possible in C# 9. The proposal is already checked in. You can verify in Language Feature Status - C# 9 when it will become available in a preview version.

In the detailed design section of the proposal, it says:

Otherwise, determine whether the type 'X' has an appropriate GetEnumerator extension method

using System;
using System.Collections.Generic;

public static class MyExtensions
{
    // Note: ranges aren't intended to work like this. It's just an example.
    public static IEnumerable GetEnumerator(this Range range)
    {
        // .. do validation ..
        for (var i = range.Start.Value; i <= range.End.Value; i++)
        {
            yield return i;
        }
    }
}

public class ExtensionGetEnumerator
{

    public void Method()
    {
        var range = 1..2;
        foreach (var i in range.GetEnumerator())
        {
            Console.WriteLine($"Print with explicit GetEnumerator {i}");
        }

        // The feature is in progress, scheduled for C# 9, the below does not compile yet

        //foreach (var i in range)
        //{
        //    Console.WriteLine($"Print with implicit GetEnumerator {i}");
        //}
    }
}