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  1. using System;
  2. using System.Linq;
  3. using System.Reflection;
  4. using System.Linq.Expressions;
  5. using System.Collections.Generic;
  6. using System.Collections.Concurrent;
  7.  
  8. public static class AnonymousObjectMutator
  9. {
  10.     private const BindingFlags FieldFlags = BindingFlags.NonPublic | BindingFlags.Instance;
  11.     private const BindingFlags PropFlags = BindingFlags.Public | BindingFlags.Instance;
  12.     private static readonly string[] BackingFieldFormats = { "<{0}>i__Field", "<{0}>" };
  13.     private static ConcurrentDictionary<Type, IDictionary<string, Action<object, object>>> _map =
  14.         new ConcurrentDictionary<Type, IDictionary<string, Action<object, object>>>();
  15.  
  16.     public static T Set<T, TProperty>(
  17.         this T instance, 
  18.         Expression<Func<T, TProperty>> propExpression,
  19.         TProperty newValue) where T : class
  20.     {
  21.         GetSetterFor(propExpression)(instance, newValue);
  22.         return instance;
  23.     }
  24.  
  25.     private static Action<object, object> GetSetterFor<T, TProperty>(Expression<Func<T, TProperty>> propExpression)
  26.     {
  27.         var memberExpression = propExpression.Body as MemberExpression;
  28.         if (memberExpression == null || memberExpression.Member.MemberType != MemberTypes.Property)
  29.             throw new InvalidOperationException("Only property expressions are supported");
  30.         Action<object, object> setter = null;
  31.         GetPropMap<T>().TryGetValue(memberExpression.Member.Name, out setter);
  32.         if (setter == null)
  33.             throw new InvalidOperationException("No setter found");
  34.         return setter;
  35.     }
  36.  
  37.     private static IDictionary<string, Action<object, object>> GetPropMap<T>()
  38.     {
  39.         return _map.GetOrAdd(typeof(T), x => BuildPropMap<T>());
  40.     }
  41.  
  42.     private static IDictionary<string, Action<object, object>> BuildPropMap<T>()
  43.     {
  44.         var typeMap = new Dictionary<string, Action<object, object>>();
  45.         var fields = typeof(T).GetFields(FieldFlags);
  46.         foreach (var pi in typeof(T).GetProperties(PropFlags)) 
  47.         {
  48.             var backingFieldNames = BackingFieldFormats.Select(x => string.Format(x, pi.Name)).ToList();
  49.             var fi = fields.FirstOrDefault(f => backingFieldNames.Contains(f.Name) && f.FieldType == pi.PropertyType);
  50.             if (fi == null)
  51.                 throw new NotSupportedException(string.Format("No backing field found for property {0}.", pi.Name));
  52.             typeMap.Add(pi.Name, (inst, val) => fi.SetValue(inst, val));
  53.         }
  54.         return typeMap;
  55.     }
  56. }
  57.  
  58. public class Program
  59. {
  60. 	public static void Main()
  61. 	{
  62.         var myAnonInstance = new { 
  63.             FirstField = "Hello", 
  64.             AnotherField = 30, 
  65.         };
  66.         Console.WriteLine(myAnonInstance);
  67.  
  68.         myAnonInstance
  69.             .Set(x => x.FirstField, "Hello SO")
  70.             .Set(x => x.AnotherField, 42);
  71.         Console.WriteLine(myAnonInstance);
  72. 	}
  73. }
Success #stdin #stdout 0.08s 24800KB
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{ FirstField = Hello, AnotherField = 30 }
{ FirstField = Hello SO, AnotherField = 42 }
https://ideone.com/ALG9DE
language:
C# (gmcs 5.20.1)
created:
9 years ago
visibility:
public

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