CastExtensions.cs

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using System;
using System.Linq;
using System.Reflection;
 
namespace CommandLine
{
    internal static class CastExtensions
    {
        private const string ImplicitCastMethodName = "op_Implicit";
        private const string ExplicitCastMethodName = "op_Explicit";
 
        public static bool CanCast<T>(this Type baseType)
        {
            return baseType.CanImplicitCast<T>() || baseType.CanExplicitCast<T>();
        }
 
        public static bool CanCast<T>(this object obj)
        {
            Type objType = obj.GetType();
 
            return objType.CanCast<T>();
        }
 
        public static T Cast<T>(this object obj)
        {
            try
            {
                return (T)obj;
            }
            catch (InvalidCastException)
            {
                if (obj.CanImplicitCast<T>())
                {
                    return obj.ImplicitCast<T>();
                }
 
                if (obj.CanExplicitCast<T>())
                {
                    return obj.ExplicitCast<T>();
                }
 
                throw;
            }
        }
 
        private static bool CanImplicitCast<T>(this Type baseType)
        {
            return baseType.CanCast<T>(ImplicitCastMethodName);
        }
 
        private static bool CanImplicitCast<T>(this object obj)
        {
            Type baseType = obj.GetType();
 
            return baseType.CanImplicitCast<T>();
        }
 
        private static bool CanExplicitCast<T>(this Type baseType)
        {
            return baseType.CanCast<T>(ExplicitCastMethodName);
        }
 
        private static bool CanExplicitCast<T>(this object obj)
        {
            Type baseType = obj.GetType();
 
            return baseType.CanExplicitCast<T>();
        }
 
        private static bool CanCast<T>(this Type baseType, string castMethodName)
        {
            Type targetType = typeof(T);
 
            return baseType.GetMethods(BindingFlags.Public | BindingFlags.Static)
                           .Where(mi => mi.Name == castMethodName && mi.ReturnType == targetType)
                           .Any(mi =>
                                {
                                    ParameterInfo pi = mi.GetParameters()
                                                         .FirstOrDefault();
 
                                    return pi != null && pi.ParameterType == baseType;
                                }
                               );
        }
 
        private static T ImplicitCast<T>(this object obj)
        {
            return obj.Cast<T>(ImplicitCastMethodName);
        }
 
        private static T ExplicitCast<T>(this object obj)
        {
            return obj.Cast<T>(ExplicitCastMethodName);
        }
 
        private static T Cast<T>(this object obj, string castMethodName)
        {
            Type objType = obj.GetType();
 
            MethodInfo conversionMethod = objType.GetMethods(BindingFlags.Public | BindingFlags.Static)
                                                 .Where(mi => mi.Name == castMethodName && mi.ReturnType == typeof(T))
                                                 .SingleOrDefault(mi =>
                                                                  {
                                                                      ParameterInfo pi = mi.GetParameters()
                                                                          .FirstOrDefault();
 
                                                                      return pi != null && pi.ParameterType == objType;
                                                                  }
                                                                 );
 
            if (conversionMethod != null)
            {
                return (T)conversionMethod.Invoke(null,
                                                  new[] { obj }
                                                 );
            }
 
            throw new InvalidCastException($"No method to cast {objType.FullName} to {typeof(T).FullName}");
        }
    }
}