C#•9mo ago

❔ Are there read only collections that don't box enumerators?

ReadOnlyCollection<T> boxes struct enumerators since it stores IList<T> internally. ImmutableList<T> does not box enumerator, but I actually want to publically expose a List as read only and privately be able to modify it.

7 Replies

reflectronic•9mo ago

you mean, like, a collection type which wraps another collection type, which does not box the enumerator through GetEnumerator? it is not possible to write something like that in C#. there is no abstraction which allows for that

nathanAjacobs•9mo ago

Yes exactly

reflectronic•9mo ago

i mean. it is possible to make your own IFastEnumerable<T, TEnumerator> interface or whatever. it would be possible using an interface like that. but List does not implement that interface

nathanAjacobs•9mo ago

I mean couldn't something like this achieve it?

public class ReadOnlyList<T> : IReadOnlyList<T>, IList<T>, IList
{
    private readonly List<T> _list;

    public ReadOnlyList(List<T> list)
    {
        if (list is null)
            throw new ArgumentNullException(nameof(list));

        _list = list;
    }

    public List<T>.Enumerator GetEnumerator()
    {
        return _list.GetEnumerator();
    }
}

public class ReadOnlyList<T> : IReadOnlyList<T>, IList<T>, IList
{
    private readonly List<T> _list;

    public ReadOnlyList(List<T> list)
    {
        if (list is null)
            throw new ArgumentNullException(nameof(list));

        _list = list;
    }

    public List<T>.Enumerator GetEnumerator()
    {
        return _list.GetEnumerator();
    }
}

It basically is what ReadOnlyCollection<T> is but instead of storing IList<T> it stores List<T> internally

reflectronic•9mo ago

oh, i see. i thought you wanted something that worked for any IList<T> without boxing but, no, there isn't a class in the BCL with a struct enumerator that wraps another collection

nathanAjacobs•9mo ago

Yeah I thought so, I'll just have to implement these manually then. Ty!

Accord•9mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Are there read only collections that don't box enumerators?