René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Constructor failing argument matching, silently selects default constructor","articleBody":"(Version 2.1)\n\nGiven .NET class:\n\n``` C#\n      public class A {\n\n           public A() { a=1.0;}\n\n           public A(double ax) { a=ax;}\n\n           public double a;\n\n     }\n```\n\nthen in python:\n\n``` python\nfrom Xxx import A\n\na1 = A(2)   # surprise! default constructor is selected, silently, basically because \n            # there is no int-\u003edouble type promotion in constructor binder\n            # causing first bind to fail, then second bind with no args (that was a fix\n            # to allow .NET objects to be super-classes (or be sub-classed) from\n            # python succeeds..\na2 = A(2.0) # Ok, now we get the second constructor, because it's a perfect match.\n```\n\nI am fully aware that super-classes, argument-matching, (automatic) type-conversion,\n and bridging the gap between python and .NET (C#) , is very complex.\nAnd providing a full implementation that 'just do the thing we want' is not trivial.\n\nIt might be that some of the issues related to sub-classing, as well as argument matching/conversion is related, - but I hope the simple example above illustrates that\nsome minor improvement at this stage could be quite useful.\n\nThere is a few fixes, that could improve this slightly:\n\n(a.) Make simple type-promotion/argument conversion happen during constructor argument matching\n(b.) If construction of a .NET object is attempted, and argument match fail, then always raise Type error\n\nI will provide a PR for (a.) since it's a simple fix to verify a simple type-promotion from int-\u003edouble etc.\n\nFixing (b.), raise error if no .NET constructor matches the arguments is easy, but will then break the sub-class mechanism. If we knew, by the time we are calling the .NET constructor, that it's a super-class, then we  _could_ either have a relaxed matching (as is to day, default to the default-ct, if fail), and then insist on match for all other cases.\n\nAfter all, providing something that fixes (b.), and at the same time supports, and possibly extends super()/sub-classing mechanism seems harder to me, since we need to know the context in which the .NET object is constructed.\n\nIf anyone see a easy solution to (b.) , - as in knowing how to get the context of the .NET class construction, that would be great.\n\nWe could then provide a  fix where \n\n' you succeed with your intention creating a new object with the supplied parameters, and get the expected result, or we raise Type-exception notifying about the problem' \n","author":{"url":"https://github.com/sigbjorn","@type":"Person","name":"sigbjorn"},"datePublished":"2016-07-03T22:09:47.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":9},"url":"https://github.com/238/pythonnet/issues/238"}