DevExpress CodeRush Tips&Tricks

There are two interesting refactorings shipped in Refactor! Pro:

• Compress to Null Coalescing Operation
• Expand Null Coalescing Operation

The first one converts a ternary expression into an equivalent null coalescing operation. The second one is the opposite of the first one – it converts a null coalescing operation to an equivalent ternary expression. Both refactorings are available in CSharp only, because Visual Basic, for example, doesn’t have a null coalescing operator.

Here’s an excerpt from the C# language specification about the null coalescing operator for reference:

• A null coalescing expression of the form a ?? b requires a to be of a nullable type or reference type. If a is non-null, the result of a ?? b is a; otherwise, the result is b. The operation evaluates b only if a is null.
• The null coalescing operator is right-associative, meaning that operations are grouped from right to left. For example, an expression of the form a ?? b ?? c is evaluated as a ?? (b ?? c). In general terms, an expression of the form E1 ?? E2 ?? … ?? EN returns the first of the operands that is non-null, or null if all operands are null.

So, the null coalescing operator provides an effective, compact way to check whether a value is null, and if so, return an alternative value. For example:

Brush myBrush = GetCachedBrush() ?? new SolidBrush(Color.Black);

In the code above, if the return value of GetCachedBrush() is not null, it is assigned to the myBrush variable. Otherwise, if it is null, a new SolidBrush is created and assigned.

The ?? operator is also useful for output. For example, instead of using the ternary operator,

String userName = GetUserName();
Console.WriteLine(userName != null ? userName : "User doesn't exist.");

You can apply the Compress to Null Coalescing Operation refactoring:

(click on the image to see it in the original size)

and use the null coalescing operator instead:

String userName = GetUserName();
Console.WriteLine(userName ?? "User doesn't exist.");

The Expand Null Coalescing Operation can be useful when you would like to change the condition of the check, for example. From a null check to something different, e.g.:

Console.WriteLine(userName != String.Empty ? userName : "User name is undefined.");

The preview hint of the refactoring will show you the resulting code before you apply it:

(click on the image to see it in the original size)

Similar Posts:

• Code Issues hints for expressions
• Refactorings that work with strings – Use IsNullOrEmpty
• Changing an explicit cast-expression to an ‘as’ operator and back
• How to get the declaring element (declaration) from a reference using DXCore
• String.Format-specific refactorings shipped in Refactor! Pro