Question

Consider the code below:

#if DEBUG
    if (Systems.Contains(system))
        throw new InvalidOperationException("System already registered");
#endif

    Debug.Assert(!Systems.Contains(system), "System already registered");

Previously I used to do the former, I’ve since discovered Debug.Assert.

Is there a reason why I should not always prefer Debug.Assert?

1. It only exists in debug code (it has the attribute [Conditional("DEBUG")]).
2. It seems to me to be more suited to my intention (code sanity checks, rather than raising exceptions to be handled later).
3. It’s less code to write.

Answer 1

You can always use Debug.Assert(), because this class is complied with the DEBUG conditional as well:

[Conditional("Debug")]

Indicates to compilers that a method call or attribute should be
ignored unless a specified conditional compilation symbol is defined.

ConditionalAttribute is applied to the methods that are defined in the
Debug and Trace classes.
http://msdn.microsoft.com/en-us/library/system.diagnostics.conditionalattribute.aspx