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Some recent project work in C# unearthed a few grains of syntactic sugar which I thought deserved a quick post. Not necessarily because they are ground breaking discoveries, but more because I found it difficult to find information via the usual channels (google) and wanted to share. I think the poor information discovery is a result of said features being based on the question mark which is not an easy symbol to use for searches online.

Single Question Mark – nullable types

The single question mark syntax is somewhat obscure. Essentially it is short hand syntax for marking primitives as nullable. System.Nullable is a generic struct that is essentially a wrapper to signify nullability. This can be used as shown below:

// a nullable type for int
int? thing = 12;

// is syntactically equivalent to
System.Nullable<int> otherThing = 12;

// can be any valid int value OR null
thing = -12;
thing = null;

// usage
//y is set to zero
int y = thing.GetValueOrDefault();
// but this will throw an exception as thing.HasValue == false
y = thing.Value;

Double Question Mark – non null assignment precedence

This one is a little obscure but can be quite handy, it is very similar to certain assignment constructs in Perl as it allows one to use precedence to assign a variable from other potential variables and is a nice way to deal with default values.

String thing = null;
String defaultThing = "nothing";

// standard trinary syntax
String otherThing = (thing != null) ? thing : defaultThing;

// syntactic sugar for the above
String sugaredThing = thing ?? defaultThing;

// can also chain things
otherThing = null;

// the first non-null value is the result of the assignment
String anotherThing = thing ?? otherThing ?? defaultThing;

// if all potentials are null, then the assignement is null)
anotherThing = thing ?? otherThing;

Tags: c#, dotnet, newbies

This entry was posted on Tuesday, April 28th, 2009 at 11:27:34 and is filed under Blog, Development, Technology, Under the hood. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.