当我期望相等的两个值不相等时抛出什么异常？ （C＃）

Question

I feel like this has to be a duplicate, but I've tried looking around and can't find what I'm looking for.

The example I'm working with starts with parsing an XML document. In this XML document the name of a person is stated in two different locations. Later in a different method, I need to use this person's name. I can use any of these two references to the person's name in the XML document since they are the same, or so I expect. I first want to check that they are indeed the same. If they are not equal for whatever reason, I feel like it would be best to throw an exception. Is there an exception for when two values that one would expect are equal are not in fact equal?

I considered ArgumentException , but I'm not sure if that's best since it specifies:

ArgumentException is thrown when a method is invoked and at least one of the passed arguments does not meet the parameter specification of the called method.

This isn't the case here since the arguments are fine, it's just that the value of one of the properties (ie the person's name) is not what I expect it to be.

I suppose the first question you might have is why do I want to throw an exception. Maybe it's not the best option, but I feel it should be done considering that the reason the two names do not match is because when the XML document was created one of the name-writes did not do its job correctly, which I'd probably want to know. I'm not experienced with error handling, so it's possible that this doesn't mean an exception should be thrown. Any advice would be appreciated.

Answer 1

I first want to check that they are indeed the same. If they are not equal for whatever reason, I feel like it would be best to throw an exception.

You could use InvalidOperationException , since your operation expects the values to be equal. If the values are not equal, your operation is invalid.

You could also define your own exception. You can afterward customize your exception in regards of your situation / objects to compare.

Answer 2

Instead of an exception, this should be a code contract : your code couldn't work if input XML has provided name twice. It's a requirement of your code to work properly .

Thus, I would create a List<string> at the beginning of your method, and I would accumulate found names in the XML. Once you need to use the whole name, I would check the list with a code contract:

Contract.Assert(names != null && names.Count > 0);
Contract.Assert(names.Skip(1).All(name => name == names[0]));