Read-only list or unmodifiable list in .NET 4.0
From what I can tell, .NET 4.0 still lacks read-only lists. Why does the framework still lack this functionality? Isn't this one of the commonest pieces of functionality for domain-driven design?
One of the few advantages Java has over C# is this in the form of the Collections.unmodifiablelist(list) method, which it seems is long overdue in IList<T> or List<T>.
Using IEnumerable<T>
is the easiest solution to the question - ToList
can be used and returns a copy.
Solution 1:
You're looking for ReadOnlyCollection
, which has been around since .NET2.
IList<string> foo = ...;
// ...
ReadOnlyCollection<string> bar = new ReadOnlyCollection<string>(foo);
or
List<string> foo = ...;
// ...
ReadOnlyCollection<string> bar = foo.AsReadOnly();
This creates a read-only view, which reflects changes made to the wrapped collection.
Solution 2:
For those who like to use interfaces:
.NET 4.5 adds the generic IReadOnlyList
interface which is implemented by List<T>
for example.
It is similar to IReadOnlyCollection
and adds an Item
indexer property.
Solution 3:
How about the ReadOnlyCollection already within the framework?
Solution 4:
If the most common pattern of the list is to iterate through all the elements, IEnumerable<T>
or IQueryable<T>
can effectively act as a read-only list as well.