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Lazy Alternatives - LazyAndWeak and BackgroundLoader

, 1 Dec 2011
This article will present two alternatives to Lazy.
LazyAlternatives.zip
LazyAlternatives
LazyAlternatives.suo
LazyAlternativesSample
Properties
Settings.settings
Pfz
Caching
Collections
DataTypes
DynamicObjects
Internal
Extensions
Factoring
Pfz.csproj.user
Pfz.Phone.csproj.user
Pfz.ruleset
Pfz.Silverlight.csproj.user
Pfz.snk
Pfz.suo
PhoneSpecific
Properties
Remoting
Instructions
Internal
Serializers
Udp
Serialization
BinaryBuiltIn
Threading
Contexts
Disposers
Unsafe
using System;
using System.Collections.Generic;
using System.Reflection;
using Pfz.DynamicObjects.Internal;
using Pfz.Extensions;

namespace Pfz.DynamicObjects
{
	/// <summary>
	/// Class responsable for casting objects to an interface type that they don't support, but have equivalent methods.
	/// </summary>
	public static class StructuralCaster
	{
		#region Cast
			private static HashSet<KeyValuePair<Type, Type>> _validatedTypes = new HashSet<KeyValuePair<Type, Type>>();

			/// <summary>
			/// Casts an object to a given type.
			/// </summary>
			public static T Cast<T>(object source, object securityToken=null)
			{
				if (source == null)
					return default(T);

				if (source is T)
				{
					T result = (T)source;
					return result;
				}

				var baseDuck = source as BaseDuck;
				if (baseDuck != null)
					return baseDuck.StructuralCast<T>(securityToken);

				if (!typeof(T).IsInterface)
					throw new ArgumentException("Cast to " + typeof(T).FullName + " is not valid.");

				return _Cast<T>(source, securityToken);
			}

			internal static T _Cast<T>(object source, object securityToken)
			{
				Type type = source.GetType();
				var pair = new KeyValuePair<Type, Type>(typeof(T), type);

				lock (_validatedTypes)
				{
					if (!_validatedTypes.Contains(pair))
					{
						_Validate(false, typeof(T), type);

						foreach (var baseInterface in typeof(T).GetInterfaces())
							_Validate(false, baseInterface, type);

						_validatedTypes.Add(pair);
					}
				}

				return DuckCaster._FinalCast<T>(source, type, securityToken);
			}
		#endregion
		#region GetStaticInterface
			private static readonly Dictionary<KeyValuePair<Type, Type>, object> _staticInterfaces = new Dictionary<KeyValuePair<Type, Type>, object>();

			/// <summary>
			/// Gets the static methods of a type into an interface.
			/// </summary>
			public static T GetStaticInterface<T>(Type typeWithStaticMembers)
			{
				if (typeWithStaticMembers == null)
					throw new ArgumentNullException("typeWithStaticMembers");

				if (!typeof(T).IsInterface)
					throw new ArgumentException(typeof(T).FullName + " is not an interface type.");

				T result;
				var key = new KeyValuePair<Type, Type>(typeof(T), typeWithStaticMembers);
				lock(_staticInterfaces)
				{
					object untypedResult;
					if (_staticInterfaces.TryGetValue(key, out untypedResult))
						return (T)untypedResult;

					// First we need to validate the static properties, methods and events, so
					// we at least have when we try to get the object, if the static class is invalid, instead
					// of having an exception when calling a method or property.
					_Validate(true, typeof(T), typeWithStaticMembers);

					foreach(var baseInterface in typeof(T).GetInterfaces())
						_Validate(true, baseInterface, typeWithStaticMembers);

					result = (T)DuckCaster._GetStaticInterface<T>(typeWithStaticMembers, key);
					_staticInterfaces.Add(key, result);
				}

				return result;
			}
		#endregion

		#region _Validate
			private static void _Validate(bool expectStatic, Type interfaceType, Type toType)
			{
				if (!expectStatic)
					if (interfaceType.IsAssignableFrom(toType))
						return;

				_ValidateProperties(expectStatic, interfaceType, toType);
				_ValidateEvents(expectStatic, interfaceType, toType);
				_ValidateMethods(expectStatic, interfaceType, toType);
			}

			private static void _ValidateMethods(bool expectStatic, Type interfaceType, Type toType)
			{
				foreach (var fromMethodInfo in interfaceType.GetMethods())
				{
					if (fromMethodInfo.IsSpecialName)
						continue;

					string methodName = fromMethodInfo.Name;

					Type[] parameterTypes = fromMethodInfo.GetParameterTypes();

					Type otherReturnType;

					MethodBase toMethod;
					if (fromMethodInfo.ContainsCustomAttribute<CallConstructorAttribute>())
					{
						if (!expectStatic)
							throw new ArgumentException("Method " + methodName + " of type " + toType.FullName + " must call a constructor, but this is not valid for Casts.");

						if (fromMethodInfo.IsGenericMethodDefinition)
							throw new ArgumentException("Method " + methodName + " of type " + toType.FullName + " is a generic method definition, that must call a constructor. Generic method definitions can't call constructors.");

						var constructor = toType.GetCompatibleConstructor(true, true, parameterTypes);

						if (constructor == null)
							throw new ArgumentException(toType.FullName + " does not have a compatible constructor for " + methodName + ".");

						otherReturnType = toType;

						toMethod = constructor;
					}
					else
					{
						BindingFlags bindingFlags;
						if (expectStatic)
							bindingFlags = BindingFlags.Public | BindingFlags.Static;
						else
							bindingFlags = BindingFlags.Public | BindingFlags.Instance;

						MethodInfo toMethodInfo = toType.GetCompatibleMethod(methodName, bindingFlags, true, true, parameterTypes); ;

						if (toMethodInfo == null)
							throw new ArgumentException(toType.FullName + " does not have a method " + methodName + " with compatible parameter types.");

						if (toMethodInfo.IsGenericMethodDefinition)
							if (DuckCaster._MakeGenericMethod(fromMethodInfo, toMethodInfo) == null)
								throw new ArgumentException("Method " + methodName + " of interface " + interfaceType.FullName + " can't call the method with the same name on " + toType.FullName + ".");

						otherReturnType = toMethodInfo.ReturnType;
						toMethod = toMethodInfo;

						if (toMethod.IsStatic != expectStatic)
						{
							if (expectStatic)
								throw new ArgumentException("Method " + methodName + " of type " + toType.FullName + " is not static.");
							else
								throw new ArgumentException("Method " + methodName + " of type " + toType.FullName + " is static.");
						}

					}

					Type[] toParameterTypes = toMethod.GetParameterTypes();
					for (int i = 0; i < toParameterTypes.Length; i++)
					{
						var fromParameterType = parameterTypes[i];
						var toParameterType = toParameterTypes[i];

						if (fromParameterType.IsByRef != toParameterType.IsByRef)
							throw new ArgumentException("Parameter at index " + i + " from method " + methodName + " of type " + interfaceType.FullName + " has a ByRef different than the real class.");
					}

					Type returnType = fromMethodInfo.ReturnType;
					if (fromMethodInfo.ContainsCustomAttribute<CastAttribute>())
					{
						if (returnType == typeof(void))
							throw new ArgumentException("Method " + methodName + " of interface type " + interfaceType.FullName + " does not returns a value, but is marked with [CastResultAttribute].");

						if (!returnType.IsInterface)
							throw new ArgumentException("Method " + methodName + " of interface type " + interfaceType.FullName + " is marked with [CastResultAttribute], but its result is not an interface type.");
					}
					else
					{
						if (returnType != typeof(void))
							if (!returnType.IsGenericParameter && !otherReturnType.IsGenericParameter)
								if (!returnType.IsAssignableFrom(otherReturnType) && !otherReturnType.IsAssignableFrom(returnType))
									throw new ArgumentException("Method " + methodName + " of type " + toType.FullName + " does not have a compatible return type.");
					}
				}
			}

			private static void _ValidateEvents(bool expectStatic, Type interfaceType, Type toType)
			{
				foreach (var eventInfo in interfaceType.GetEvents())
				{
					string eventName = eventInfo.Name;
					var toEvent = toType.GetEvent(eventName);

					if (toEvent == null)
						throw new ArgumentException(toType.FullName + " does not have an event named " + eventName + ".");

					if (toEvent.GetAddMethod().IsStatic != expectStatic)
					{
						if (expectStatic)
							throw new ArgumentException("Event " + eventName + " of type " + toType.FullName + " is not static.");
						else
							throw new ArgumentException("Event " + eventName + " of type " + toType.FullName + " is static.");
					}

					Type eventType = eventInfo.EventHandlerType;
					if (eventType != toEvent.EventHandlerType)
						throw new ArgumentException("Event " + eventName + " of type " + toType.FullName + " is not of type " + eventType.FullName + ".");
				}
			}

			private static void _ValidateProperties(bool expectStatic, Type interfaceType, Type toType)
			{
				foreach (var propertyInfo in interfaceType.GetProperties())
				{
					string propertyName = propertyInfo.Name;
					var toProperty = toType.GetProperty(propertyName);

					Type propertyType = propertyInfo.PropertyType;

					if (toProperty == null)
					{
						_ValidateField(expectStatic, toType, propertyInfo, propertyName, propertyType);

						continue;
					}

					if (toProperty.GetAccessors()[0].IsStatic != expectStatic)
					{
						if (expectStatic)
							throw new ArgumentException("Property " + propertyName + " of type " + toType.FullName + " is not static.");
						else
							throw new ArgumentException("Property " + propertyName + " of type " + toType.FullName + " is static.");
					}

					Type staticPropertyType = toProperty.PropertyType;
					if (!propertyType.IsAssignableFrom(staticPropertyType) && !staticPropertyType.IsAssignableFrom(propertyType))
						if (!((propertyType.IsEnum && staticPropertyType == typeof(string)) || (staticPropertyType.IsEnum && propertyType == typeof(string))))
							throw new ArgumentException("Property " + propertyName + " of type " + toType.FullName + " does not has a return type compatible with " + propertyType.FullName + ".");

					if (propertyInfo.CanRead && !toProperty.CanRead)
						throw new ArgumentException("Property " + propertyName + " of type " + toType.FullName + " does not have a read accessor.");

					if (propertyInfo.CanWrite && !toProperty.CanWrite)
						throw new ArgumentException("Property " + propertyName + " of type " + toType.FullName + " does not have a write accessor.");

					var parameters1 = propertyInfo.GetIndexParameters();
					var parameters2 = toProperty.GetIndexParameters();

					int length = parameters1.Length;
					if (length != parameters2.Length)
						throw new ArgumentException("Property " + propertyName + " of type " + toType.FullName + " has an invalid index parameter count.");

					for (int i = 0; i < length; i++)
					{
						var parameterInfo1 = parameters1[i];
						var parameterInfo2 = parameters2[i];

						if (!parameterInfo2.ParameterType.IsAssignableFrom(parameterInfo1.ParameterType) && !parameterInfo1.ParameterType.IsAssignableFrom(parameterInfo2.ParameterType))
							throw new ArgumentException("Indexed parameter " + i + " of property " + propertyName + " of type " + toType.FullName + " has an invalid type.");
					}
				}
			}

			private static void _ValidateField(bool expectStatic, Type toType, PropertyInfo propertyInfo, string propertyName, Type propertyType)
			{
				var staticField = toType.GetField(propertyName);

				if (staticField == null)
					throw new ArgumentException(toType.FullName + " does not have a property or field named " + propertyName + ".");

				if (staticField.IsStatic != expectStatic)
				{
					if (expectStatic)
						throw new ArgumentException("Field " + propertyName + " of type " + toType.FullName + " is not static.");
					else
						throw new ArgumentException("Field " + propertyName + " of type " + toType.FullName + " is static.");
				}

				if (!propertyType.IsAssignableFrom(staticField.FieldType) && !staticField.FieldType.IsAssignableFrom(propertyType))
					throw new ArgumentException("Field " + propertyName + " of type " + toType.FullName + " does not has a return type compatible with " + propertyType.FullName + ".");

				if (staticField.IsInitOnly || staticField.IsLiteral)
				{

					if (propertyInfo.CanWrite)
						throw new ArgumentException("Field " + propertyName + " of type " + toType.FullName + " is read-only.");
				}

				if (propertyInfo.GetIndexParameters().Length != 0)
					throw new ArgumentException("Field " + propertyName + " of type " + toType.FullName + " can't be used to implement an indexed property.");
			}
		#endregion
	}
}

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License

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About the Author

Paulo Zemek
Architect
Canada Canada
I started to program computers when I was 11 years old, as a hobbist, programming in AMOS Basic and Blitz Basic for Amiga.
At 12 I had my first try with assembler, but it was too difficult at the time. Then, in the same year, I learned C and, after learning C, I was finally able to learn assembler (for Motorola 680x0).
Not sure, but probably between 12 and 13, I started to learn C++. I always programmed "in an object oriented way", but using function pointers instead of virtual methods.
 
At 15 I started to learn Pascal at school and to use Delphi. At 16 I started my first internship (using Delphi). At 18 I started to work professionally using C++ and since then I've developed my programming skills as a professional developer in C++ and C#, generally creating libraries that help other developers do they work easier, faster and with less errors.
 
Want more info or simply want to contact me?
Take a look at: http://paulozemek.azurewebsites.net/
Or e-mail me at: paulozemek@outlook.com
 
Codeproject MVP 2012
Microsoft MVP 2013

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