{"id":1023,"date":"2009-11-05T23:46:00","date_gmt":"2009-11-05T23:46:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/vbteam\/2009\/11\/05\/spot-the-bug-much-ado-about-nothing-part-2-jonathan-aneja\/"},"modified":"2024-07-05T12:42:35","modified_gmt":"2024-07-05T19:42:35","slug":"spot-the-bug-much-ado-about-nothing-part-2-jonathan-aneja","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/vbteam\/spot-the-bug-much-ado-about-nothing-part-2-jonathan-aneja\/","title":{"rendered":"Spot the Bug! – Much ado about Nothing… Part 2! (Jonathan Aneja)"},"content":{"rendered":"

In yesterday’s<\/a> post we saw that the use of the wrong comparison operator with Nothing in an If block can lead to surprising results.  <\/span>Let’s look at a slightly different case today:<\/font><\/p>\n

\n

 <\/font><\/p>\n<\/p>\n

        <\/span>Dim<\/span> x As<\/span> Integer<\/span> = Nothing<\/p>\n

<\/span><\/span><\/p>\n

<\/p>\n

 <\/p>\n

<\/span><\/p>\n

        <\/span>If<\/span> x = Nothing<\/span> Then<\/p>\n

<\/span><\/span><\/p>\n

            <\/span>MsgBox(“A true statement – we land here”<\/span>)<\/p>\n

<\/span><\/p>\n

        <\/span>Else<\/p>\n

<\/span><\/span><\/p>\n

            <\/span>MsgBox(“The statement is a lie – we land here”<\/span>)<\/p>\n

<\/span><\/p>\n

        <\/span>End<\/span> If<\/span><\/span><\/p>\n

\n

 <\/font><\/p>\n<\/p>\n

What gets printed?  <\/span>If the code is intended to print “A true statement…”, is there actually a bug in this code?<\/p>\n

<\/i><\/font><\/font><\/p>\n

\n

 <\/font><\/p>\n<\/p>\n

\n

 <\/font><\/p>\n<\/p>\n

.<\/font><\/p>\n

\n

 <\/font><\/p>\n<\/p>\n

.<\/font><\/p>\n

\n

 <\/font><\/p>\n<\/p>\n

.<\/font><\/p>\n

\n

 <\/font><\/p>\n<\/p>\n

.<\/font><\/p>\n

\n

 <\/font><\/p>\n<\/p>\n

.<\/font><\/p>\n

<\/p>\n

 <\/font><\/p>\n

<\/b><\/p>\n

Answer:  <\/span><\/b>The code is correct according to its “specification” (I’m using the term loosely here <\/font>J<\/span><\/span>), so from a technical point of view there is no bug here.   <\/span>However<\/i>, from a code readability and maintenance point of view, I’d argue that there is a bug.<\/font><\/font><\/p>\n

\n

 <\/font><\/p>\n<\/p>\n

The Nothing literal in VB means “default value for this type”, and for an Integer that would be 0.  <\/span>So the code above is exactly<\/i> equivalent to this:<\/font><\/p>\n

\n

 <\/font><\/p>\n<\/p>\n

    <\/span>Dim<\/span> x As<\/span> Integer<\/span> = 0<\/p>\n

<\/span><\/span><\/p>\n

<\/p>\n

 <\/p>\n

<\/span><\/p>\n

    <\/span>If<\/span> x = 0 Then<\/p>\n

<\/span><\/span><\/p>\n

        <\/span>MsgBox(“A true statement – we land here”<\/span>)<\/p>\n

<\/span><\/p>\n

    <\/span>Else<\/p>\n

<\/span><\/span><\/p>\n

 \n       <\/span>MsgBox(“The statement is a lie – we land here”<\/span>)<\/p>\n

<\/span><\/p>\n

    <\/span>End<\/span> If<\/span><\/span><\/p>\n

\n

 <\/font><\/p>\n<\/p>\n

Now that’s way <\/i>more readable than the version above, and dramatically reduces the potential for confusion.  <\/span>In general*, if you ever find yourself writing “= Nothing” in a conditional expression, you should either be changing the = to “Is” (as we saw yesterday), or you should change Nothing to the actual default value if possible.  <\/span><\/font><\/font><\/p>\n

<\/span><\/font><\/font> <\/p>\n

<\/p>\n

The next post will have a real bug, I promise J<\/span><\/span><\/font><\/p>\n

<\/span><\/span><\/font> <\/p>\n

<\/p>\n

*Yes, there may be cases such as structure\/generics\/overloaded operators where you actually would want to say “= Nothing” – my point is that if you’re going to do this make sure you know what you’re doing, and insert a comment so that those reading your code also know what you’re doing <\/font><\/span><\/i>J<\/span><\/span><\/i>.<\/p>\n

<\/font><\/span><\/i><\/p>\n

<\/span><\/span><\/font><\/span><\/font><\/p>\n","protected":false},"excerpt":{"rendered":"

In yesterday’s post we saw that the use of the wrong comparison operator with Nothing in an If block can lead to surprising results.  Let’s look at a slightly different case today:           Dim x As Integer = Nothing           If x = Nothing Then             MsgBox(“A true statement – we land here”) […]<\/p>\n","protected":false},"author":260,"featured_media":8818,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[195],"tags":[83,143,165,166,167],"class_list":["post-1023","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-visual-basic","tag-jonathan-aneja","tag-spot-the-bug","tag-vb2005","tag-vb2008","tag-vb2010"],"acf":[],"blog_post_summary":"

In yesterday’s post we saw that the use of the wrong comparison operator with Nothing in an If block can lead to surprising results.  Let’s look at a slightly different case today:           Dim x As Integer = Nothing           If x = Nothing Then             MsgBox(“A true statement – we land here”) […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/posts\/1023","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/users\/260"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/comments?post=1023"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/posts\/1023\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/media\/8818"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/media?parent=1023"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/categories?post=1023"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/tags?post=1023"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}