How to Get the Count of an IEnumerable without Iteration?

Obtaining the Count of IEnumerable without Iteration

In certain scenarios, developers may need to ascertain the count of elements within an IEnumerable collection without the necessity of iterating through it. This arises, for instance, when a progress status needs to be displayed by indicating the current and total number of items being processed.

However, IEnumerable lacks an inherent method to retrieve the count without iteration. This is a deliberate design choice, as IEnumerable embraces lazy evaluation, only generating elements as they are requested.

Solution: Utilizing ICollection

To circumvent the limitation of IEnumerable, developers can leverage ICollection, which inherits from IEnumerable and includes a Count property. By casting the IEnumerable instance to ICollection, the Count property can be directly accessed, providing the number of elements without requiring iteration.

Example:

Consider the following code:

private IEnumerable<string> Tables
{
    get
    {
        yield return "Foo";
        yield return "Bar";
    }
}

To determine the count of tables without iterating, the code can be modified as follows:

var count = ((ICollection<string>)Tables).Count;

The cast to ICollection enables direct access to the Count property, yielding the value of 2, indicating the number of tables in the collection without the need for iteration.

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