Question

A library function parses a file and returns an object. If a parser encounters unknown data, missing values etc., it shouldn’t throw an exception and stop parsing (because this is not fatal), but there should be a way to pass information about these things to a caller (so that warnings can be displayed in the UI, for example). How can these warning be returned? I’m thinking of passing a callback function/object into the library, are there any other possible solutions?

Answer 1

I would have a collection of errors easily accessible on the parser, something like this:

public class Parser
{
   public bool HasErrors { 
     get { return ParseErrors != null && ParseErrors.Count > 0; } 
   }    
   public List<string> ParseErrors { get; set; }
   public object Parse(string fileName) {}
}

Or whatever error type you wanted of course, something with more detail maybe.

Code calling your library would look something like this:

var p = new Parser();
var o = p.Parse("file.txt"); //Get object
if(p.HasErrors) //Uh oh, abort, do something with p.ParseErrors