Sieve/Sieve/Extensions/MethodInfoExtended.cs

using System;
using System.Reflection;

namespace Sieve.Extensions
{
    // The default GetMethod doesn't allow for generic methods which means
    // custom filters for different sources can't share the same name.
    // https://stackoverflow.com/questions/4035719/getmethod-for-generic-method
    public static partial class MethodInfoExtended
    {
        /// <summary>
        /// Search for a method by name and parameter types.  
        /// Unlike GetMethod(), does 'loose' matching on generic
        /// parameter types, and searches base interfaces.
        /// </summary>
        /// <exception cref="AmbiguousMatchException"/>
        public static MethodInfo GetMethodExt(this Type thisType,
                                                string name,
                                                Type firstType)
        {
            return GetMethodExt(thisType,
                                name,
                                BindingFlags.Instance
                                | BindingFlags.Static
                                | BindingFlags.Public
                                | BindingFlags.NonPublic
                                | BindingFlags.FlattenHierarchy,
                                firstType);
        }

        /// <summary>
        /// Search for a method by name, parameter types, and binding flags.  
        /// Unlike GetMethod(), does 'loose' matching on generic
        /// parameter types, and searches base interfaces.
        /// </summary>
        /// <exception cref="AmbiguousMatchException"/>
        public static MethodInfo GetMethodExt(this Type thisType,
                                                string name,
                                                BindingFlags bindingFlags,
                                                Type firstType)
        {
            MethodInfo matchingMethod = null;

            // Check all methods with the specified name, including in base classes
            GetMethodExt(ref matchingMethod, thisType, name, bindingFlags, firstType);

            // If we're searching an interface, we have to manually search base interfaces
            if (matchingMethod == null && thisType.IsInterface)
            {
                foreach (Type interfaceType in thisType.GetInterfaces())
                    GetMethodExt(ref matchingMethod,
                                 interfaceType,
                                 name,
                                 bindingFlags,
                                 firstType);
            }

            return matchingMethod;
        }

        private static void GetMethodExt(ref MethodInfo matchingMethod,
                                            Type type,
                                            string name,
                                            BindingFlags bindingFlags,
                                            Type firstType)
        {
            // Check all methods with the specified name, including in base classes
            foreach (MethodInfo methodInfo in type.GetMember(name,
                                                             MemberTypes.Method,
                                                             bindingFlags))
            {
                // Check that the parameter counts and types match, 
                // with 'loose' matching on generic parameters
                ParameterInfo[] parameterInfos = methodInfo.GetParameters();

                if (parameterInfos[0].ParameterType.IsSimilarType(firstType))
                {
                    if (matchingMethod == null)
                        matchingMethod = methodInfo;
                    else
                        throw new AmbiguousMatchException(
                                "More than one matching method found!");
                }
            }
        }

        /// <summary>
        /// Special type used to match any generic parameter type in GetMethodExt().
        /// </summary>
        public class T
        { }

        /// <summary>
        /// Determines if the two types are either identical, or are both generic 
        /// parameters or generic types with generic parameters in the same
        ///  locations (generic parameters match any other generic paramter,
        /// but NOT concrete types).
        /// </summary>
        private static bool IsSimilarType(this Type thisType, Type type)
        {
            // Ignore any 'ref' types
            if (thisType.IsByRef)
                thisType = thisType.GetElementType();
            if (type.IsByRef)
                type = type.GetElementType();

            // Handle array types
            if (thisType.IsArray && type.IsArray)
                return thisType.GetElementType().IsSimilarType(type.GetElementType());

            // If the types are identical, or they're both generic parameters 
            // or the special 'T' type, treat as a match
            if (thisType == type || ((thisType.IsGenericParameter || thisType == typeof(T))
                                 && (type.IsGenericParameter || type == typeof(T))))
                return true;

            // Handle any generic arguments
            if (thisType.IsGenericType && type.IsGenericType)
            {
                Type[] thisArguments = thisType.GetGenericArguments();
                Type[] arguments = type.GetGenericArguments();
                if (thisArguments.Length == arguments.Length)
                {
                    for (int i = 0; i < thisArguments.Length; ++i)
                    {
                        if (!thisArguments[i].IsSimilarType(arguments[i]))
                            return false;
                    }
                    return true;
                }
            }

            return false;
        }
    }
}