Modifying values directly using LINQ?

Question

Is it possible to modify elements of a collection, say List, LinkedList, etc using something like:

collection.Do ( action )

which does something like:

item.Value = 0
(for each item)

I know enumerators only give the value, not the reference, hence the question.

How would one do this using LINQ?

Answer 1

Try:

void ModifyEach<T>(this IList<T> list, Func<T, T> modifier)
{
    for (int n = 0; n < list.Count; n++)
        list[n] = modifier(list[n]);
}

Usage:

List<int> x = new List<int> { 1, 3, 7 };

x.ModifyEach(n => n + 1); // increment each item

Answer 2

If your collection contains reference types then you can modify its items in-place by using an extension method, similar to the ForEach method on List<T>.

This is possible because you're not actually trying to alter the IEnumerable<T> sequence: The collection contains references but you're only modifying the referenced objects, not the references themselves.

This technique won't work for collections of value types. In that case you would be trying to alter the read-only, IEnumerable<T> sequence, which isn't possible.

public static void ForEach<T>(this IEnumerable<T> source, Action<T> action)
{
    foreach (T item in source)
    {
        action(item);
    }
}

// ...

public class Example
{
    public int Value { get; set; }
}

// ...

Example[] examples =
    {
        new Example { Value = 1 }, new Example { Value = 2 },
        new Example { Value = 3 }, new Example { Value = 4 }
    };

examples.ForEach(x => x.Value *= 2);

// displays 2, 4, 6, 8
foreach (Example e in examples)
{
    Console.WriteLine(e.Value);
}