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Lazy Alternatives - LazyAndWeak and BackgroundLoader

, 1 Dec 2011 CPOL 10.3K 296 25
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.Linq.Expressions;
using System.Reflection;

namespace Pfz
{
	/// <summary>
	/// This class allows you to get members from types more safely than using
	/// string literals. It only exists because C# does not have fieldinfoof,
	/// propertyinfoof and methodinfoof.
	/// </summary>
	public static class ReflectionHelper
	{
		#region GetMember
			/// <summary>
			/// Gets a member by it's expression usage.
			/// For example, GetMember(() => obj.GetType()) will return the
			/// GetType method.
			/// </summary>
			public static MemberInfo GetMember<T>(Expression<Func<T>> expression)
			{
				if (expression == null)
					throw new ArgumentNullException("expression");
				
				var body = expression.Body;
			
				switch(body.NodeType)
				{
					case ExpressionType.MemberAccess:
						MemberExpression memberExpression = (MemberExpression)body;
						return memberExpression.Member;
				
					case ExpressionType.Call:
						MethodCallExpression callExpression = (MethodCallExpression)body;
						return callExpression.Method;
				
					case ExpressionType.New:
						NewExpression newExpression = (NewExpression)body;
						return newExpression.Constructor;
				}
			
				throw new ArgumentException("expression.Body must be a member or call expression.", "expression");
			}
		#endregion
		#region GetConstructor
			/// <summary>
			/// Gets the constructor info from a sample construction call expression.
			/// Example: GetConstructor(() => new Control()) will return the constructor
			/// info for the default constructor of Control.
			/// </summary>
			public static ConstructorInfo GetConstructor<T>(Expression<Func<T>> expression)
			{
				return (ConstructorInfo)GetMember(expression);
			}
		#endregion
		#region GetField
			/// <summary>
			/// Gets a field from a sample usage.
			/// Example: GetField(() => Type.EmptyTypes) will return the FieldInfo of
			/// EmptyTypes.
			/// </summary>
			public static FieldInfo GetField<T>(Expression<Func<T>> expression)
			{
				return (FieldInfo)GetMember(expression);
			}
		#endregion
		#region GetProperty
			/// <summary>
			/// Gets a property from a sample usage.
			/// Example: GetProperty(() => str.Length) will return the property info 
			/// of Length.
			/// </summary>
			public static PropertyInfo GetProperty<T>(Expression<Func<T>> expression)
			{
				return (PropertyInfo)GetMember(expression);
			}
		#endregion
		#region GetMethod
			/// <summary>
			/// Gets a method info of a void method.
			/// Example: GetMethod(() => Console.WriteLine("")); will return the
			/// MethodInfo of WriteLine that receives a single argument.
			/// </summary>
			public static MethodInfo GetMethod(Expression<Action> expression)
			{
				if (expression == null)
					throw new ArgumentNullException("expression");
			
				var body = expression.Body;
				if (body.NodeType != ExpressionType.Call)
					throw new ArgumentException("expression.Body must be a Call expression.", "expression");
			
				MethodCallExpression callExpression = (MethodCallExpression)body;
				return callExpression.Method;
			}
		
			/// <summary>
			/// Gets the MethodInfo of a method that returns a value.
			/// Example: GetMethod(() => Console.ReadLine()); will return the method info
			/// of ReadLine.
			/// </summary>
			public static MethodInfo GetMethod<T>(Expression<Func<T>> expression)
			{
				return (MethodInfo)GetMember(expression);
			}
		#endregion
	}

	/// <summary>
	/// This is a typed version of reflection helper, so your expression already starts with a know
	/// object type (used when you don't have an already instantiated object).
	/// </summary>
	public static class ReflectionHelper<ForType>
	{
		#region GetMember
			/// <summary>
			/// Gets a member by it's expression usage.
			/// For example, GetMember((obj) => obj.GetType()) will return the
			/// GetType method.
			/// </summary>
			public static MemberInfo GetMember<T>(Expression<Func<ForType, T>> expression)
			{
				if (expression == null)
					throw new ArgumentNullException("expression");
				
				var body = expression.Body;
			
				switch(body.NodeType)
				{
					case ExpressionType.MemberAccess:
						MemberExpression memberExpression = (MemberExpression)body;
						return memberExpression.Member;
				
					case ExpressionType.Call:
						MethodCallExpression callExpression = (MethodCallExpression)body;
						return callExpression.Method;
				
					case ExpressionType.New:
						NewExpression newExpression = (NewExpression)body;
						return newExpression.Constructor;
				}
			
				throw new ArgumentException("expression.Body must be a member or call expression.", "expression");
			}
		#endregion
		#region GetField
			/// <summary>
			/// Gets a field from a sample usage.
			/// Example: GetField((obj) => obj.SomeField) will return the FieldInfo of
			/// EmptyTypes.
			/// </summary>
			public static FieldInfo GetField<T>(Expression<Func<ForType, T>> expression)
			{
				return (FieldInfo)GetMember(expression);
			}
		#endregion
		#region GetProperty
			/// <summary>
			/// Gets a property from a sample usage.
			/// Example: GetProperty((str) => str.Length) will return the property info 
			/// of Length.
			/// </summary>
			public static PropertyInfo GetProperty<T>(Expression<Func<ForType, T>> expression)
			{
				return (PropertyInfo)GetMember(expression);
			}
		#endregion
		#region GetMethod
			/// <summary>
			/// Gets a method info of a void method.
			/// Example: GetMethod((obj) => obj.SomeCall("")); will return the
			/// MethodInfo of SomeCall that receives a single argument.
			/// </summary>
			public static MethodInfo GetMethod(Expression<Action<ForType>> expression)
			{
				if (expression == null)
					throw new ArgumentNullException("expression");
			
				var body = expression.Body;
				if (body.NodeType != ExpressionType.Call)
					throw new ArgumentException("expression.Body must be a Call expression.", "expression");
			
				MethodCallExpression callExpression = (MethodCallExpression)body;
				return callExpression.Method;
			}
		
			/// <summary>
			/// Gets the MethodInfo of a method that returns a value.
			/// Example: GetMethod((obj) => obj.SomeCall()); will return the method info
			/// of SomeCall.
			/// </summary>
			public static MethodInfo GetMethod<T>(Expression<Func<ForType, T>> expression)
			{
				return (MethodInfo)GetMember(expression);
			}
		#endregion
	}
}

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About the Author

Paulo Zemek
Engineer Microsoft Corporation
United States United States
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.

Now I just started working as a Senior Software Engineer at Microsoft.

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, 2015
Microsoft MVP 2013-2014

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