.net - Does LINQ work with IEnumerable?


I have a class that implements IEnumerable, but doesn't implement IEnumerable<T>. I can't change this class, and I can't use another class instead of it. As I've understood from MSDN LINQ can be used if class implements IEnumerable<T>. I've tried using instance.ToQueryable(), but it still doesn't enable LINQ methods. I know for sure that this class can contain instances of only one type, so the class could implement IEnumerable<T>, but it just doesn't. So what can I do to query this class using LINQ expressions?

All Answers
  • Translate

    You can use Cast<T>() or OfType<T> to get a generic version of an IEnumerable that fully supports LINQ.


    IEnumerable objects = ...;
    IEnumerable<string> strings = objects.Cast<string>();

    Or if you don't know what type it contains you can always do:

    IEnumerable<object> e = objects.Cast<object>();

    If your non-generic IEnumerable contains objects of various types and you are only interested in eg. the strings you can do:

    IEnumerable<string> strings = objects.OfType<string>();

  • Translate

    Yes it can. You just need to use the Cast function to get it to convert to a typed IEnumerable<T>. For example

    IEnumerable e = ...;
    IEnumreable<object> e2 = e.Cast<object>();

    Now e2 is an IEnumerable<T> and can work with all LINQ functions.

  • Translate

    You can also use LINQ's query comprehension syntax, which casts to the type of the range variable (item in this example) if a type is specified:

    IEnumerable list = new ArrayList { "dog", "cat" };
    IEnumerable<string> result =
      from string item in list
      select item;
    foreach (string s in result)
        // InvalidCastException at runtime if element is not a string

    The effect is identical to @JaredPar's solution; see Explicit Range Variable Types in the C# language specification for details.