What is a read only collection?

Question

I ran a security code analyst i found myself having a CA2105 warning. I looked at the grade tampering example. I didn't realize you can assign int[] to a readonly int. I thought readonly was like the C++ const and makes it illegal.

The How to Fix Violations suggest i clone the object (which i don't want to do) or 'Replace the array with a strongly typed collection that cannot be changed'. I clicked the link and see 'ArrayList' and adding each element one by one and it doesn't look like you can prevent something adding more.

So when i have this piece of code what is the easiest or best way to make it a read only collection?

public static readonly string[] example = { "a", "b", "sfsdg", "sdgfhf", "erfdgf", "last one"};

Answer 1

var readOnly = new ReadOnlyCollection<string>(example);

Answer 2

public static readonly ReadOnlyCollection<string> example
    = new ReadOnlyCollection<string>(new string[] { "your", "options", "here" });

(although it should still probably be exposed as a get property rather than a public field)

Answer 3

ReadOnlyCollection<string> readOnlyCollection = 
            new ReadOnlyCollection<string>(example);

Answer 4

The easiest way to have a collection which you cannot modify is to use

ReadOnlyCollection

Example from MSDN:

List<string> dinosaurs = new List<string>();
dinosaurs.Add("Tyrannosaurus");
dinosaurs.Add("Amargasaurus");
dinosaurs.Add("Deinonychus");
dinosaurs.Add("Compsognathus");

ReadOnlyCollection<string> readOnlyDinosaurs = new ReadOnlyCollection<string>(dinosaurs);

Answer 5

If you're working with arrays, you can use

return Array.AsReadOnly(example);

to wrap your array in a read-only collection.