Expanding an array by one

Question

I have a class filtercollection which holds a collection of Filters:

class TransactionTypeFilterCollection
{
    public CategoryNode FilterCollection { get; private set; }
    public TransactionTypeFilter[] Filters { get; private set; }
    public void AddFilter(string field, FilterOperator filterOperator, string value)
    {
        TransactionTypeFilter newFilter = new TransactionTypeFilter(
            filterCollection: this.FilterCollection,
            name: this.FilterCollection.Name + "_Filter_" + this.Filters.Length,
            field: field,
            filterOperator: filterOperator,
            value: value
        );
        TransactionTypeFilter[] newFilterCollection = new TransactionTypeFilter[this.Filters.Length+1];
        Array.Copy(this.Filters, 0, newFilterCollection,0, this.Filters.Length);
        newFilterCollection[this.Filters.Length] = newFilter;
        this.Filters = newFilterCollection;
    }
}

Specifically I am not using a List for elements cannot easily be added/removed from outside without accessing the proper function of the Filter Collection. Also for Performance reasons.

This code to extend the array feels somewhat cumbersome to me and does not "feel" right:

TransactionTypeFilter[] newFilterCollection = new TransactionTypeFilter[this.Filters.Length+1];
Array.Copy(this.Filters, 0, newFilterCollection,0, this.Filters.Length);
newFilterCollection[this.Filters.Length] = newFilter;
this.Filters = newFilterCollection;

I normally would do something like the following:

List<TransactionTypeFilter> newFilterCollection = this.Filters.ToList();
newFilterCollection.Add(newFilter);
this.Filters = newFilterCollection.ToArray();

But benchmarking showed that array.Copy is faster by a factor of 3~ and the result of method 2 gets worse the more elements I want to add.

Even with a plane List where I add elements, method 1 was faster.

Is there a better way to expand the array?

I found an answer in Is it possible to extend arrays in C#? but when trying Array.Resize in my class, I receive the compiler error: A property or Indexer may not be passed as out or ref parameter.

Answer 1

Are you passing in the reference parameter correctly? The error indicates that you are trying to pass in a property. Properties are not variables and therefore cannot be passed as out parameters. This might work for your usages

private static Array ResizeArray(Array arr, int[] newSizes)
{
   var temp = Array.CreateInstance(arr.GetType().GetElementType(), newSizes);
   int length = arr.Length <= temp.Length ? arr.Length : temp.Length;
   Array.ConstrainedCopy(arr, 0, temp, 0, length);
   return temp;
}