Eric Yin Eric Yin - 1 year ago 191
C# Question

Does C# have IsNullOrEmpty for List/IEnumerable?

I know generally empty List is more prefer than NULL. But I am going to return NULL, for mainly two reasons

  1. I have to check and handle null values explicitly, avoiding bugs and attacks.

  2. It is easy to perform
    operation afterwards to get a return value.

For strings, we have IsNullOrEmpty. Is there anything from C# itself doing the same thing for List or IEnumerable?

Answer Source

nothing baked into the framework, but it's a pretty straight forward extension method.

See here

/// <summary>
    /// Determines whether the collection is null or contains no elements.
    /// </summary>
    /// <typeparam name="T">The IEnumerable type.</typeparam>
    /// <param name="enumerable">The enumerable, which may be null or empty.</param>
    /// <returns>
    ///     <c>true</c> if the IEnumerable is null or empty; otherwise, <c>false</c>.
    /// </returns>
    public static bool IsNullOrEmpty<T>(this IEnumerable<T> enumerable)
        if (enumerable == null)
            return true;
        /* If this is a list, use the Count property for efficiency. 
         * The Count property is O(1) while IEnumerable.Count() is O(N). */
        var collection = enumerable as ICollection<T>;
        if (collection != null)
            return collection.Count < 1;
        return !enumerable.Any(); 

Daniel Vaughan takes the extra step of casting to ICollection (where possible) for performance reasons. Something I would not have thought to do.

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