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Posted 23 Aug 2011
Licenced CPOL

C# Automatic Property Default Value Extension Methods

, 23 Aug 2011
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For .NET 4.0:using System;using System.Collections.Generic;using System.ComponentModel;using System.Reflection;using System.Linq.Expressions;static class AutomaticPropertyExtensions{ private static class Cache where T : class { public static readonly...
For .NET 4.0:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Reflection;
using System.Linq.Expressions;

static class AutomaticPropertyExtensions
    private static class Cache<T> where T : class
        public static readonly Action<T> Init;
        public static readonly int PropertyCount;

        static Cache()
            var p = Expression.Parameter(typeof(T), "this");
            var body = Expression.Block(typeof(T)
                .Select(pair => Assign(p, pair.Item1, pair.Item2)));

            PropertyCount = body.Expressions.Count;
            if (PropertyCount != 0)
                var result = Expression.Lambda<Action<T>>(body, p);
                Init = result.Compile();
    private static Expression Assign(Expression p, PropertyInfo property, object value)
        var prop = Expression.Property(p, property);
        var defaultValue = Expression.Constant(value, property.PropertyType);
        return Expression.Assign(prop, defaultValue);
    private static IEnumerable<Tuple<PropertyInfo, object>> ListPropertiesToReset(this Type componentType)
        const BindingFlags flags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic;

        return from PropertyInfo property in componentType.GetProperties(flags)
               where property.CanWrite
               let attributes = property.GetCustomAttributes(typeof(DefaultValueAttribute), true)
               where attributes != null && 0 != attributes.Length
               let attribute = (DefaultValueAttribute)attributes[0]
               let defaultValue = attribute.Value
               where defaultValue != null
               select Tuple.Create(property, defaultValue);

    public static int ResetPropsUsingDefaultAttributes<T>(this T instance) where T : class
        if (instance == null) throw new ArgumentNullException("instance");
        if (Cache<T>.Init != null) Cache<T>.Init(instance);
        return Cache<T>.PropertyCount;

public class TestClass
    public double MyPie { get; set; }

    public string MyLove { get; set; }

    public TestClass()

    public void Reset()

    public override string ToString()
        return string.Format("MyPie = {0}, MyLove = {1}",
            MyPie, MyLove == null ? "null" : MyLove);


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Richard Deeming
Software Developer Nevalee Business Solutions
United Kingdom United Kingdom
No Biography provided

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Comments and Discussions

GeneralReason for my vote of 5 Quite an improvement. Doesn't look a... Pin
Itai Basel23-Aug-11 12:29
memberItai Basel23-Aug-11 12:29 

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