Showing a proposed use of Guard with expression for static checks and correct name evaluation in exception messages

Guard.cs

public static class Guard
{
	public static void NotNull<T>(Expression<Func<T>> notNullableExpression) where T : class
	{
		var compliedExpression = notNullableExpression.Compile();
		if (compliedExpression() == null)
		{
			var paramName = notNullableExpression.GetObjectNameGraph();
			throw new ArgumentNullException(paramName);
		}
	}
	
	public static void NotNullOrWhiteSpace(Expression<Func<string>> notNullableExpression) 
	{
		var compliedExpression = notNullableExpression.Compile();
		if (string.IsNullOrWhiteSpace(compliedExpression()))
		{
			var paramName = notNullableExpression.GetObjectNameGraph();
			throw new ArgumentException("Must not be null or empty/whitepsace string", paramName);
		}
	}
	
	public static void Require<T>(Expression<Func<T>> notNullableExpression, Expression<Predicate<T>> predicate) where T : class
	{
		var x = notNullableExpression.Compile();
		if (!predicate.Compile()((x())))
		{
			var paramName = notNullableExpression.GetObjectNameGraph();
			throw new ArgumentException("failed predicate : " + predicate.ToString(), paramName);
		}
	}
}

public static class PropertyNameEx
{
	public static string GetObjectNameGraph<T>(this Expression<Func<T>> propertyExpression)
	{
		var lambda = propertyExpression as LambdaExpression;
		if(lambda == null) 
			throw new Exception("Must be a LambdaExpression");
		return string.Concat(GetPropertyNames(lambda.Body).Intersperse("."));
	}
	
	private static IEnumerable<string> GetPropertyNames(Expression expression)
	{
		var memberExpression = expression as MemberExpression;
		if (memberExpression == null) yield break;
	
		var member = memberExpression.Member as MemberInfo;//Lambda syntax may make the initial value a field (in a closure i assume)
		if (member == null)
		{
			memberExpression.Member.Dump("Error");
			throw new Exception("Expression member is not a property or field accessor");
		}
		foreach (var propertyName in GetPropertyNames(memberExpression.Expression))
		{
			yield return propertyName;
		} 
		yield return member.Name;
	}

	private static IEnumerable<T> Intersperse<T>(this IEnumerable<T> items, T separator)
	{
		var first = true;
		foreach (var item in items)
		{
			if (first) 
				first = false;
			else
				yield return separator;
			yield return item;
		}
	}	
}

SampleUsageOfGuard.cs

void Main()
{
	var message = new { Alpha = "A", Beta = (string)null, Gamma = new { Delta = "Hi"}};
	var messageConcrete  = new TestObj();
	messageConcrete.Testy = "Franco";
	try{
		Guard.NotNull(()=>message);
		Guard.NotNullOrWhiteSpace(()=>message.Gamma.Delta);
		Guard.NotNull(()=>messageConcrete.Testy);
		Guard.Require(()=>messageConcrete.Testy, t=> t == "Arnold");//abitary prdeicate
	}
	catch(Exception ex)
	{
		ex.Dump();
	}
	
	message = new { Alpha = "A", Beta = (string)null, Gamma = new { Delta = (string)null}};
	
	try
	{
		Guard.NotNullOrWhiteSpace(()=>message.Gamma.Delta);
	}
	catch(Exception ex)
	{
		ex.Dump();
	}
}

public class TestObj
{
	public string Testy;//fields work ok
}