Home/ Questions/Q 827949
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-15T03:39:08+00:00

Possible Duplicate: C# Cannot convert from IEnumerable<Base> to IEnumerable<Derived> I have D1 and D2

  • 0

Possible Duplicate:
C# Cannot convert from IEnumerable<Base> to IEnumerable<Derived>

I have D1 and D2 which derive from B. When i write var ls = (IEnumerable<B>)(cond?lsD1:lsD2); I get a runtime cast error. IIRC this is a well known problem. My question is

1) Is this allowed yet? perhaps in .NET 4? I have 2010 but my project is a few months old, large and targets 3.5.

2) Is there a simple workaround? I only need to read the list not add anything or remove. Actually, ToArray() would probably work but is there another solution?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    So if I’m reading your question correctly, this is an example of covarience. C# 4 supports this for some interfaces IEnumerable being one of them.

    The workaround in C# 3 would probably be something along the lines of:

    var ls = (IEnumerable<B>)(cond ? lsD1.Cast<B>() : lsD2.Cast<B>());

    Turning them into arrays would also work, but only because variance is "broken" (see section: Broken array variance) for arrays.

    • 0