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/*
Add these:
using System.Collections.Generic;
using System.Reflection;
using System.Reflection.Emit;
*/
void Main()
{
WriteDeltas(new Foo { X = 123, Y = DateTime.Today, Z = null },
new Foo { X = 124, Y = DateTime.Today, Z = null });
WriteDeltas(new Foo { X = 123, Y = DateTime.Today, Z = null },
new Foo { X = 123, Y = DateTime.Now, Z = new Dummy() });
}
static void WriteDeltas<T>(T x, T y)
{
Console.WriteLine("----");
foreach (string delta in PropertyComparer<T>.GetDeltas(x, y))
Console.WriteLine(delta);
}
class Dummy { }
class Foo
{
public int X { get; set; }
public DateTime Y { get; set; }
public Dummy Z { get; set; }
}
public static class PropertyComparer<T>
{
private static readonly Func<T, T, List<string>> getDeltas;
static PropertyComparer()
{
var dyn = new DynamicMethod(":getDeltas", typeof(List<string>), new[] { typeof(T), typeof(T) }, typeof(T));
var il = dyn.GetILGenerator();
// create a new list of strings
il.Emit(OpCodes.Newobj, typeof(List<string>)
.GetConstructor(Type.EmptyTypes));
// access the 'Add' method of the generic List<>
var add = typeof(List<string>).GetMethod("Add");
foreach (var prop in typeof(T).GetProperties())
{
if (!prop.CanRead) continue;
Label next = il.DefineLabel();
switch (Type.GetTypeCode(prop.PropertyType))
{
case TypeCode.Boolean:
case TypeCode.Byte:
case TypeCode.Char:
case TypeCode.Double:
case TypeCode.Int16:
case TypeCode.Int32:
case TypeCode.Int64:
case TypeCode.SByte:
case TypeCode.Single:
case TypeCode.UInt16:
case TypeCode.UInt32:
case TypeCode.UInt64:
// generates something like 'return x.prop == y.prop;'
il.Emit(OpCodes.Ldarg_0); // x
il.EmitCall(OpCodes.Callvirt, prop.GetGetMethod(), null); // .prop
il.Emit(OpCodes.Ldarg_1); // y
il.EmitCall(OpCodes.Callvirt, prop.GetGetMethod(), null); // .prop
il.Emit(OpCodes.Ceq); // ==
break;
default:
var pp = new Type[] { prop.PropertyType, prop.PropertyType };
var eq = prop.PropertyType.GetMethod("op_Equality", BindingFlags.Public | BindingFlags.Static, null, pp, null);
// Try to get the '==' comparater
if (eq != null)
{
il.Emit(OpCodes.Ldarg_0); // x
il.EmitCall(OpCodes.Callvirt, prop.GetGetMethod(), null); // .prop
il.Emit(OpCodes.Ldarg_1); // y
il.EmitCall(OpCodes.Callvirt, prop.GetGetMethod(), null); // .prop
il.EmitCall(OpCodes.Call, eq, null); // ==
}
else
{
il.EmitCall(OpCodes.Call,
typeof(EqualityComparer<>)
.MakeGenericType(prop.PropertyType)
.GetProperty("Default")
.GetGetMethod(),
null); // .Equals()
il.Emit(OpCodes.Ldarg_0); // x
il.EmitCall(OpCodes.Callvirt, prop.GetGetMethod(), null); // .prop
il.Emit(OpCodes.Ldarg_1); // y
il.EmitCall(OpCodes.Callvirt, prop.GetGetMethod(), null); // .prop
il.EmitCall(OpCodes.Callvirt, typeof(EqualityComparer<>).MakeGenericType(prop.PropertyType).GetMethod("Equals", pp), null);
}
break;
}
// add the result to the List<string>
il.Emit(OpCodes.Brtrue_S, next);
il.Emit(OpCodes.Dup);
il.Emit(OpCodes.Ldstr, prop.Name);
il.EmitCall(OpCodes.Callvirt, add, null);
il.MarkLabel(next);
}
il.Emit(OpCodes.Ret); // return
getDeltas = (Func<T, T, List<string>>)dyn.CreateDelegate(typeof(Func<T, T, List<string>>));
}
public static List<string> GetDeltas(T x, T y) { return getDeltas(x, y); }
}
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