IsNull Extension Method

Date Published: 02 July 2008

IsNull Extension Method

I’m strongly considering adopting the use of an IsNull extension method in my .NET 3.5 coding projects. A quick search to see what others have to say about this revealed a new web site dedicated to extension methods, which includes this IsNull method ready to go:

<span style="color: #0000ff">public static</span> <span style="color: #0000ff">bool</span> IsNull(<span style="color: #0000ff">this</span> <span style="color: #0000ff">object</span> source)

{

  <span style="color: #0000ff">return</span> source == <span style="color: #0000ff">null</span>;
}

The String class supports the IsNullOrEmpty() method now, but you have to pass it your instance yourself. This is another good candidate for Extension Method treatment. Brad Wilson posted about this earlier this year, and received some good comments, none of which seem to indicate that these are evil or icky.

From the ExtensionMethod.Net site, here is an example of the String check that I use so frequently:

<span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">bool</span> IsNotNullOrEmpty(<span style="color: #0000ff">this</span> <span style="color: #0000ff">string</span> input) {

    <span style="color: #0000ff">return</span> !String.IsNullOrEmpty(input);

}

There are actually quite a few cool ones for strings. I think I like having Format as an extension as well:

<span style="color: #0000ff">using</span> System;
<span style="color: #0000ff">using</span> System.Linq
<span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">class</span> StringExtensions

{

    <span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">string</span> Format(<span style="color: #0000ff">this</span> <span style="color: #0000ff">string</span> format, <span style="color: #0000ff">object</span> arg, <span style="color: #0000ff">params</span> <span style="color: #0000ff">object</span>[] additionalArgs)

    {

        <span style="color: #0000ff">if</span> (additionalArgs == <span style="color: #0000ff">null</span> || additionalArgs.Length == 0)

        {

            <span style="color: #0000ff">return</span> <span style="color: #0000ff">string</span>.Format(format, arg);

        }

        <span style="color: #0000ff">else</span>

        {

            <span style="color: #0000ff">return</span> <span style="color: #0000ff">string</span>.Format(format, <span style="color: #0000ff">new</span> <span style="color: #0000ff">object</span>[] { arg }.Concat(additionalArgs).ToArray());

        }

    }

}

Update: The Format extension method doesn’t work as-is. I’ve renamed mine to Formatx(), which works.

Steve Smith

About Ardalis

Software Engineer

Steve is an experienced software architect and trainer, focusing currently on ASP.NET Core and Domain-Driven Design.


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