这不太美观,但似乎能够工作:
public static class GroupGenerator
{
public static T Create<T>(IEnumerable<T> items) where T : class
{
return (T)Activator.CreateInstance(Cache<T>.Type, items);
}
private static class Cache<T> where T : class
{
internal static readonly Type Type;
static Cache()
{
if (!typeof(T).IsInterface)
{
throw new InvalidOperationException(typeof(T).Name
+ " is not an interface");
}
AssemblyName an = new AssemblyName("tmp_" + typeof(T).Name);
var asm = AppDomain.CurrentDomain.DefineDynamicAssembly(
an, AssemblyBuilderAccess.RunAndSave);
string moduleName = Path.ChangeExtension(an.Name,"dll");
var module = asm.DefineDynamicModule(moduleName, false);
string ns = typeof(T).Namespace;
if (!string.IsNullOrEmpty(ns)) ns += ".";
var type = module.DefineType(ns + "grp_" + typeof(T).Name,
TypeAttributes.Class | TypeAttributes.AnsiClass |
TypeAttributes.Sealed | TypeAttributes.NotPublic);
type.AddInterfaceImplementation(typeof(T));
var fld = type.DefineField("items", typeof(IEnumerable<T>),
FieldAttributes.Private);
var ctor = type.DefineConstructor(MethodAttributes.Public,
CallingConventions.HasThis, new Type[] { fld.FieldType });
var il = ctor.GetILGenerator();
il.Emit(OpCodes.Ldarg_0);
il.Emit(OpCodes.Ldarg_1);
il.Emit(OpCodes.Stfld, fld);
il.Emit(OpCodes.Ret);
foreach (var method in typeof(T).GetMethods())
{
var args = method.GetParameters();
var methodImpl = type.DefineMethod(method.Name,
MethodAttributes.Private | MethodAttributes.Virtual,
method.ReturnType,
Array.ConvertAll(args, arg => arg.ParameterType));
type.DefineMethodOverride(methodImpl, method);
il = methodImpl.GetILGenerator();
if (method.ReturnType != typeof(void))
{
il.Emit(OpCodes.Ldstr,
"Methods with return values are not supported");
il.Emit(OpCodes.Newobj, typeof(NotSupportedException)
.GetConstructor(new Type[] {typeof(string)}));
il.Emit(OpCodes.Throw);
continue;
}
var iter = il.DeclareLocal(typeof(IEnumerator<T>));
il.Emit(OpCodes.Ldarg_0);
il.Emit(OpCodes.Ldfld, fld);
il.EmitCall(OpCodes.Callvirt, typeof(IEnumerable<T>)
.GetMethod("GetEnumerator"), null);
il.Emit(OpCodes.Stloc, iter);
Label tryFinally = il.BeginExceptionBlock();
Label loop = il.DefineLabel();
il.Emit(OpCodes.Br_S, loop);
Label doItem = il.DefineLabel();
il.MarkLabel(doItem);
il.Emit(OpCodes.Ldloc, iter);
il.EmitCall(OpCodes.Callvirt, typeof(IEnumerator<T>)
.GetProperty("Current").GetGetMethod(), null);
for (int i = 0; i < args.Length; i++)
{
switch (i)
{
case 0: il.Emit(OpCodes.Ldarg_1); break;
case 1: il.Emit(OpCodes.Ldarg_2); break;
case 2: il.Emit(OpCodes.Ldarg_3); break;
default:
il.Emit(i < 255 ? OpCodes.Ldarg_S
: OpCodes.Ldarg, i + 1);
break;
}
}
il.EmitCall(OpCodes.Callvirt, method, null);
il.MarkLabel(loop);
il.Emit(OpCodes.Ldloc, iter);
il.EmitCall(OpCodes.Callvirt, typeof(IEnumerator)
.GetMethod("MoveNext"), null);
il.Emit(OpCodes.Brtrue_S, doItem);
il.Emit(OpCodes.Leave_S, tryFinally);
il.BeginFinallyBlock();
Label endFinally = il.DefineLabel();
il.Emit(OpCodes.Ldloc, iter);
il.Emit(OpCodes.Brfalse_S, endFinally);
il.Emit(OpCodes.Ldloc, iter);
il.EmitCall(OpCodes.Callvirt, typeof(IDisposable)
.GetMethod("Dispose"), null);
il.MarkLabel(endFinally);
il.EndExceptionBlock();
il.Emit(OpCodes.Ret);
}
Cache<T>.Type = type.CreateType();
#if DEBUG // for inspection purposes...
asm.Save(moduleName);
#endif
}
}
}