Best way to check for null parameters (Guard Clauses)

Question

For example, you usually don\'t want parameters in a constructor to be null, so it\'s very normal to see some thing like

if (someArg == null)
{
    throw new Arg         


        

Answer 1

public static class Ensure
{
    /// 

    /// Ensures that the specified argument is not null.
    /// 
    /// Name of the argument.
    /// The argument.
    [DebuggerStepThrough]
    [ContractAnnotation("halt <= argument:null")]        
    public static void ArgumentNotNull(object argument, [InvokerParameterName] string argumentName)
    {
        if (argument == null)
        {
            throw new ArgumentNullException(argumentName);
        }
    }
}

usage:

// C# < 6
public Constructor([NotNull] object foo)
{
    Ensure.ArgumentNotNull(foo, "foo");
    ...
}

// C# >= 6
public Constructor([NotNull] object bar)
{
    Ensure.ArgumentNotNull(bar, nameof(bar));
    ...
}

The DebuggerStepThroughAttribute comes in quite handy so that in case of an excpetion while debugging (or when I attach the debugger after the exception occurred) I will not end up inside the ArgumentNotNull method but instead at the calling method where the null reference actually happend.

I am using ReSharper Contract Annotations.

• The ContractAnnotationAttribute makes sure that I never misspell the argument ("foo") and also renames it automatically if I rename the foo symbol.
• The NotNullAttribute helps ReSharper with code analysis. So if I do new Constructor(null) if will get a warning from ReSharper that this will lead to an exception.
• If you do not like to annotate your code directly, you can also do the same thing with external XML-files that you could deploy with your library and that users can optinally reference in their ReShaprer.