Question

I am trying to do the following… (Foo is a class)

void Main() 
{
    var foos = ...
    DoSomeWork(foos);
    // I want all foos to have Bar set to 42
}

public static void DoSomeWork(IEnumberable<Foo> foos) 
{
    foreach (var foo in foos)
    {
        foo.Bar = 42;
    }
}

class Foo 
{
    String blahblah;
    Int32 Bar;
}

But all the foos have their original values. How do I change them on a ref parameter?

Answer 1

It could be that foos is a generating IEnumerable. Example:

IEnumerable<Foo> GetFoos()
{
  yield return new Foo {};
  yield return new Foo {};
  yield return new Foo {};
}

var foos = GetFoos();

You can never mutate the values being generated, as they will be freshly created each time you iterate over foos.

Now if you did the following as suggested by @YuriyRozhovetskiy, it will work.

var foos = GetFoos().ToList();

Now we can mutate happily 🙂