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    <p>Oh, yay, I get to show off something I recently wrote for something else! :)</p> <p>Caveat: This code is not the most efficient in the world, and it's VERY poorly commented - it was for a personal project, and I already knew how it worked - but I think it'll get you what you're after...</p> <p>The method you'd be most interested in would be <code>public static Tuple&lt;Type, IEnumerable&lt;Type&gt;&gt; GetCommonBases(Type left, Type right)</code></p> <p>The Tuple returned is &lt;common base class, (list of common interfaces)&gt;</p> <p>A quick summary: this class, when given a type, does the following:</p> <ul> <li><p>Reverse walks up the given type until it hits no more base types, pushing each into a 'working stack'</p></li> <li><p>Pops each base type off the working stack, inserting it into a tree-like structure; If the type implements any interfaces, it adds nodes for those interface types as well</p></li> <li><p>the helper method <code>GetCommonBases</code> creates one of these <code>TypeTree</code> structures for the first type, then 'merges' in the type tree for the other given type: it does so by walking down common base types until it finds a point where you have a common base type between the two types, at which point two branches of the tree are formed. It then "drills down" to each type from the root (i.e., <code>System.Object</code>), then finds the first point of deviation. The parent of this point of deviation is the Common base type. </p></li> <li><p>The interfaces part relies on the definition of <code>Interfaces</code>, which "inherits" any Interface nodes for any ancestor. The <code>GetCommonBases</code> method pulls a list of any interfaces implemented by the two passed in types and returns an intersection of these two lists - that is, a set of interfaces that both passed in types implement.</p></li> <li><p>the method then returns these two bits of information as a <code>Tuple&lt;Type, IEnumerable&lt;Type&gt;&gt;</code>, where the first item is the common base type, if any, and the second item is the intersection of common interfaces</p></li> </ul> <pre><code> public class TypeTree { private TypeTree() { Children = new List(); } public TypeTree(Type value) : this() { // Get to the basest class var typeChain = GetTypeChain(value).ToList(); Value = typeChain.First(); foreach (var type in typeChain.Skip(1)) { Add(type); } } public Type Value { get; private set; } public TypeTree Parent { get; private set; } public List Children { get; private set; } public IEnumerable Interfaces { get { var myInterfaces = Children.Where(c => c.Value.IsInterface); return Parent == null ? myInterfaces : myInterfaces.Concat(Parent.Interfaces).Distinct(); } } public TypeTree Find(Type type) { if (Value == type) return this; return Children.Select(child => child.Find(type)).FirstOrDefault(found => found != null); } public TypeTree Add(Type type) { TypeTree retVal = null; if (type.IsInterface) { if (Value.GetInterfaces().Contains(type)) { retVal = new TypeTree { Value = type, Parent = this }; Children.Add(retVal); return retVal; } } var typeChain = GetTypeChain(type); var walkTypes = from baseType in typeChain let alreadyExists = Value == baseType || Children.Any(c => c.Value == baseType) where !alreadyExists select baseType; foreach (var baseType in walkTypes) { if (baseType.BaseType == Value) { // Add this as a child of the current tree retVal = new TypeTree { Value = baseType, Parent = this }; Children.Add(retVal); } if (Value.IsAssignableFrom(baseType)) { // we can add this as a child, potentially retVal = Children.Aggregate(retVal, (current, child) => child.Add(baseType) ?? current); } // add interfaces var interfaces = baseType.GetInterfaces().Where(i => i != type); foreach (var intType in interfaces) { (retVal ?? this).Add(intType); } } return retVal; } public override string ToString() { var childTypeNames = Children.Select(c => c.ToString()).Distinct(); return string.Format("({0} {1})", Value.Name, string.Join(" ", childTypeNames)); } public static Tuple> GetCommonBases(Type left, Type right) { var tree = new TypeTree(left); tree.Add(right); var findLeft = tree.Find(left); var findRight = tree.Find(right); var commonInterfaces = findLeft.Interfaces.Select(i => i.Value) .Intersect(findRight.Interfaces.Select(i => i.Value)) .Distinct(); var leftStack = new Stack(); var temp = findLeft; while (temp != null) { leftStack.Push(temp); temp = temp.Parent; } var rightStack = new Stack(); temp = findRight; while (temp != null) { rightStack.Push(temp); temp = temp.Parent; } var zippedPaths = leftStack.Zip(rightStack, Tuple.Create); var result = zippedPaths.TakeWhile(tup => tup.Item1.Value == tup.Item2.Value).Last(); return Tuple.Create(result.Item1.Value, commonInterfaces); } private static IEnumerable GetTypeChain(Type fromType) { var typeChain = new Stack(); var temp = fromType; while (temp != null) { typeChain.Push(temp); temp = temp.BaseType; } return typeChain; } } </code></pre>
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    1. COI can add a description of what the class does, but other than that, the code is free for anyone's use; I just found it useful for a side project I was working on.
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