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Boxing/unboxing should be avoided - Design


Boxing is the process of converting a value type to the type object or to any interface type implemented by this value type. When the CLR boxes a value type, it wraps the value inside a System.Object and stores it on the managed heap.

Unboxing extracts the value type from the object. Boxing is implicit; unboxing is explicit.

The concept of boxing and unboxing underlies the C# unified view of the type system in which a value of any type can be treated as an object. More about boxing and unboxing here: https://msdn.microsoft.com/en-us/library/yz2be5wk.aspx

This rule has been disabled by default to avoid noise in issues found by the NDepend default rule set. If boxing/unboxing is important to your team, just re-activate this rule.

How to Fix:

Thanks to .NET generic, and especially thanks to generic collections, boxing and unboxing should be rarely used. Hence in most situations the code can be refactored to avoid relying on boxing and unboxing. See for example: http://stackoverflow.com/questions/4403055/boxing-unboxing-and-generics

With a performance profiler, indentify methods that consume a lot of CPU time. If such method uses boxing or unboxing, especially in a loop, make sure to refactor it.

By default issues of this rule have a Low severity because they reflect more an advice than a problem.