Incorrect work of SelectMany with covariance IEnumerable cast

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Incorrect work of SelectMany with covariance IEnumerable cast #353

Closed iskiselev closed 10 years ago

iskiselev commented 10 years ago

I found a problem in next example:

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

public static class Program {
    public static void Main (string[] args)
    {
        var items = GetItems()
            .SelectMany(item => new[] { item });

        foreach (var item in items)
        {
            Console.WriteLine(item.Id);
        }
    }

    private static IEnumerable<BaseClass> GetItems()
    {
        return new List<Class>() { new Class("TestItem") };
    }
}

public class BaseClass
{
    private string _id;

    public BaseClass(string id)
    {
        _id = id;
    }

    public string Id
    {
        get { return _id; }
    }}

public class Class : BaseClass
{
    public Class(string id) : base(id)
    {
    }
}

This test case fails with next error:

Error: Method 'BaseClass get_Current()' of interface 'System.Collections.Generic.IEnumerator`1[BaseClass]' is not implemented by object JSIL.ArrayEnumerator[System.Object]
(Looked for key(s): 'I47$get_Current$void=34', 
'I47$get_Current$void=53')

I'm still not sure, which implemented in JSIL libraries incorrectly (List or SelectMany method), but if I do SelectMany after covariance cast of List to IEnumerable I reproduce error. At the same time if I do the same with Class[] - it work normally.

iskiselev commented 10 years ago

Seems I found, why in this particular case I have problems. Inside SelectMany implementation there is next call:

state.currentSubsequence = JSIL.GetEnumerator(enumerable);

but inner enumerable in that case is just Array without type information (due to my item => new[] { item } inner selector). This call in that case return IEnumerator