Question

How many times we declare a simple class or struct to hold a few properties only to use them only one time when returned by a method. Way too many times I think, thankfully we always have anonymous objects which can be declared in place at run time.

With that thought in mind I would like to know how I can declare one array of such anonymous objects.

Example:

var Employee = new { ID = 5, Name= "Prashant" };

This created a anonymous object with two properties, one being integer and another string.

All good here, but how should I declare a array of this kind of object, and how would you recommend iterating through it with both a for and foreach loops.

The foreach loop is really the problem I think, because foreach loops expect a declared type. Still there might be a away, if there is I would to know it too of course.

Answer 1

[edit – updated to show population, basic enumeration, etc]

As @Eve says, LINQ is your friend here; as a general rule of thumb, don’t try passing anonymous types around – you can, if you’re clever – but it’s a HUGE pain in the butt to deal with them outside of the context/scope they were declared.

To whit, I decided to see in what ways one could “declare an array of an anonymous type” as a fun thought experiment, and came up with these:

(note: the “Dump” is due to this being written in LINQPad)

// Our anonymous type sequence
var anonymousEnumerable = Enumerable
        .Range(0, 10)
        .Select(i => new { ID = i, Text = i.ToString() });
var enumerableCount = anonymousEnumerable.Count();
var anonymousType = anonymousEnumerable.First().GetType();

// Option #1 - declare it as dynamic, i.e., anything goes
dynamic[] asDynamicArray = new dynamic[enumerableCount];
foreach(var tuple in anonymousEnumerable.Select((item, i) => Tuple.Create(i, item)))
{
    asDynamicArray[tuple.Item1] = tuple.Item2;
}

// Let's go the IEnumerable route
foreach (var asDynamic in asDynamicArray)
{
    Console.WriteLine("ID:{0} Text:{1}", asDynamic.ID, asDynamic.Text);
}

// Lowest common denominator: *everything* is an object
object[] asObjectArray = new object[enumerableCount];
foreach(var tuple in anonymousEnumerable.Select((item, i) => Tuple.Create(i, item)))
{
    asObjectArray[tuple.Item1] = tuple.Item2;
}

// Let's iterate with a for loop - BUT, it's now "untyped", so things get nasty
var idGetterMethod = anonymousType.GetMethod("get_ID");
var textGetterMethod = anonymousType.GetMethod("get_Text");
for(int i=0;i < asObjectArray.Length; i++)
{
    var asObject = asObjectArray[i];
    var id = (int)idGetterMethod.Invoke(asObject, null);
    var text = (string)textGetterMethod.Invoke(asObject, null);
    Console.WriteLine("ID:{0} Text:{1}", id, text);
}

// This is cheating :)
var letTheCompilerDecide = anonymousEnumerable.ToArray();
foreach (var item in letTheCompilerDecide)
{
    Console.WriteLine("ID:{0} Text:{1}", item.ID, item.Text);
}

// Use reflection to "make" an array of the anonymous type
var anonymousArrayType = anonymousType.MakeArrayType();
var reflectIt = Activator.CreateInstance(
          anonymousArrayType, 
          enumerableCount) as Array;    
Array.Copy(anonymousEnumerable.ToArray(), reflectIt, enumerableCount);  

// We're kind of in the same boat as the object array here, since we
// don't really know what the underlying item type is
for(int i=0;i < reflectIt.Length; i++)
{
    var asObject = reflectIt.GetValue(i);
    var id = (int)idGetterMethod.Invoke(asObject, null);
    var text = (string)textGetterMethod.Invoke(asObject, null);
    Console.WriteLine("ID:{0} Text:{1}", id, text);
}