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Defining a method with for loops and conditional statements

I have to define a method with Reflection.Emit that is rather complex, because I have to do a for loop on a field and have a condition with break and return. My method that I want to recreate with reflection looks like this in regular code:
override int GetKeyImpl(Type obj0)
{
int answer = -1;
for(int i = 0; i < knownTypes.length; i++){
if(knowntypes[i] == obj0){
answer = i;
break;
}
}
return answer;
}
My idea to solve this problem was to generate a method with reflection that redirects the call to my original method and returns the int.
I need to know how to do a for loop and breaks with OpCodes to recreate the method while doing conditional checks on an array that is inside a class. I've searched for tutorials but didn't find any that go further than addition of two ints.
Edit: Forgot to mention it, I'm using IKVM.Reflection and knownTypes is an array of Type[]. The method that im writing is one that will override an abstract one.

This should reproduce the method you specified:
TypeBuilder type = /* ... */;
FieldInfo knownFields = /* ... */;
// Finding dependencies via reflection
var baseMethod = type.BaseType.GetMethod(
"GetKeyImpl",
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
var typeEqualsOperator = typeof(Type).GetMethod(
"op_Equality",
BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic,
null,
new[] { typeof(Type), typeof(Type) },
null);
// Declaring the method
var getKeyImpl = type.DefineMethod(
baseMethod.Name,
baseMethod.Attributes & ~(MethodAttributes.Abstract |
MethodAttributes.NewSlot));
// Setting return type
getKeyImpl.SetReturnType(typeof(int));
// Adding parameters
getKeyImpl.SetParameters(typeof(Type));
getKeyImpl.DefineParameter(1, ParameterAttributes.None, "obj0");
// Override the base method
type.DefineMethodOverride(getKeyImpl, baseMethod);
var il = getKeyImpl.GetILGenerator();
// Preparing locals
var answer = il.DeclareLocal(typeof(int));
var i = il.DeclareLocal(typeof(int));
// Preparing labels
var loopCondition = il.DefineLabel();
var loopIterator = il.DefineLabel();
var returnLabel = il.DefineLabel();
var loopBody = il.DefineLabel();
// Writing body
// answer = -1
il.Emit(OpCodes.Ldc_I4_M1);
il.Emit(OpCodes.Stloc, answer);
// i = 0
il.Emit(OpCodes.Ldc_I4_0);
il.Emit(OpCodes.Stloc, i);
// jump to loop condition
il.Emit(OpCodes.Br_S, loopCondition);
// begin loop body
il.MarkLabel(loopBody);
// if (obj0 != knownTypes[i]) continue
il.Emit(OpCodes.Ldarg_0); // omit if 'knownTypes' is static
il.Emit(OpCodes.Ldfld, knownTypes); // use 'Ldsfld' if 'knownTypes' is static
il.Emit(OpCodes.Ldloc, i);
il.Emit(OpCodes.Ldelem_Ref);
il.Emit(OpCodes.Ldarg_1); // use 'Ldarg_0' if 'knownTypes' is static
il.Emit(OpCodes.Call, typeEqualsOperator);
il.Emit(OpCodes.Brfalse_S, loopIterator);
// answer = i; jump to return
il.Emit(OpCodes.Ldloc, i);
il.Emit(OpCodes.Stloc, answer);
il.Emit(OpCodes.Br_S, returnLabel);
// begin loop iterator
il.MarkLabel(loopIterator);
// i = i + 1
il.Emit(OpCodes.Ldloc, i);
il.Emit(OpCodes.Ldc_I4_1);
il.Emit(OpCodes.Add);
il.Emit(OpCodes.Stloc, i);
// begin loop condition
il.MarkLabel(loopCondition);
// if (i < knownTypes.Length) jump to loop body
il.Emit(OpCodes.Ldloc, i);
il.Emit(OpCodes.Ldarg_0); // omit if 'knownTypes' is static
il.Emit(OpCodes.Ldfld, knownTypes); // use 'Ldsfld' if 'knownTypes' is static
il.Emit(OpCodes.Ldlen);
il.Emit(OpCodes.Conv_I4);
il.Emit(OpCodes.Blt_S, loopBody);
// return answer
il.MarkLabel(returnLabel);
il.Emit(OpCodes.Ldloc, answer);
il.Emit(OpCodes.Ret);
// Finished!
The decompiled results are as expected:
override int GetKeyImpl(Type obj0)
{
for (int i = 0; i < this.knownTypes.Length; i++)
{
if (this.knownTypes[i] == obj0)
return i;
}
return -1;
}
If you have access to .NET Reflector, there is a Reflection.Emit Language Add-In that may interest you. Alternatively, write a prototype in C# code, and then run it through a disassembler to see the raw IL.
If it had been okay to make the method static (and accept knownTypes as a parameter or make it a static field), then you could have composed the method body using LINQ expression trees. Unfortunately, you cannot compose instance method bodies using this technique; they have to be static. Example:
var method = typeBuilder.DefineMethod(
"GetKeyImpl",
MethodAttributes.Private |
MethodAttributes.Static |
MethodAttributes.HideBySig);
var type = E.Parameter(typeof(Type), "type");
var knownTypes = E.Parameter(typeof(Type[]), "knownTypes");
var answer = E.Variable(typeof(int), "answer");
var i = E.Variable(typeof(int), "i");
var breakTarget = E.Label("breakTarget");
var continueTarget = E.Label("continueTarget");
var returnTarget = E.Label(typeof(int), "returnTarget");
var forLoop = E.Block(
new[] { i },
E.Assign(i, E.Constant(0)),
E.Loop(
E.Block(
E.IfThen(
E.GreaterThanOrEqual(i, E.ArrayLength(knownTypes)),
E.Break(breakTarget)),
E.IfThen(
E.Equal(E.ArrayIndex(knownTypes, i), type),
E.Return(returnTarget, i)),
E.Label(continueTarget),
E.PreIncrementAssign(i))),
E.Label(breakTarget));
var body = E.Lambda<Func<Type, Type[], int>>(
E.Block(
new[] { answer },
E.Assign(answer, E.Constant(-1)),
forLoop,
E.Label(returnTarget, answer)),
type,
knownTypes);
body.CompileToMethod(method);
return method;
The example above accepts knownTypes as the second parameter. Refactoring to read from a static field instead would be straightforward. The decompiled results, again, are as expected:
private static int GetKeyImpl(Type type, Type[] knownTypes)
{
for (int i = 0; i < knownTypes.Length; i++)
{
if (knownTypes[i] == type)
return i;
}
return -1;
}

The easist way to work out how to generate the IL for a method is to create a simple console application that has your method in. Then build it and run ILDasm against it to look at the IL instructions necessary to make up the method.
Once you can see the instructions it shouldn't be too difficult to write code to emit the OpCodes necessary.

Fast serialization and deserialization using dynamically emitted POCOs

I am currently serializing SQL table rows into a binary format for efficient storage. I serialize/deserialize the binary data into a List<object> per row. I'm trying to upgrade this to use POCOs, that will be dynamically generated (emitted) with one Field per column.
I've been searching online for hours and have stumbled upon ORMs/frameworks like EF, T4, ExpandoObject, but all of these either use a dynamic object (properties can be added/removed on the fly) or simply generate a POCO before compiling. I cannot use templating because the schema of the tables is unknown at compile time, and using dynamic objects would be overkill (and slow) since I know the exact set of properties and their types. I need to generate one POCO per table, with Fields corresponding to columns, and with the data types set accordingly (INT -> int, TEXT -> string).
After generating the POCO, I'll proceed to get/set properties using emitted CIL, much like what PetaPoco does for statically compiled POCOs. I'm hoping all of this rigmarole will be faster than using untyped Lists, and give me high-fidelity POCOs that are strongly-typed and can be accelerated by the CLR. Am I correct to assume this? and can you start me off on generating POCOs at runtime? And will using POCOs be much faster or much more memory-efficient than using a List<object>? Basically, will it be worth the trouble? I already know how to accelerate getting/setting Fields using emitted CIL.

From comments and chat, it seems that a key part of this is still creating a dynamic type; ok, here's a full example that shows a fully serializable (by any common serializer) type. You could of course add more to the type - maybe indexers to get properties by number or by name, INotifyPropertyChanged, etc.
Also - critical point: you must cache and re-use the generated Type instances. Do not keep regenerating this stuff... you will hemorrhage memory.
using Newtonsoft.Json;
using ProtoBuf;
using System;
using System.IO;
using System.Reflection;
using System.Reflection.Emit;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;
using System.Text;
using System.Xml.Serialization;
public interface IBasicRecord
{
object this[int field] { get; set; }
}
class Program
{
static void Main()
{
object o = 1;
int foo = (int)o;
string[] names = { "Id", "Name", "Size", "When" };
Type[] types = { typeof(int), typeof(string), typeof(float), typeof(DateTime?) };
var asm = AppDomain.CurrentDomain.DefineDynamicAssembly(
new AssemblyName("DynamicStuff"),
AssemblyBuilderAccess.Run);
var module = asm.DefineDynamicModule("DynamicStuff");
var tb = module.DefineType("MyType", TypeAttributes.Public | TypeAttributes.Serializable);
tb.SetCustomAttribute(new CustomAttributeBuilder(
typeof(DataContractAttribute).GetConstructor(Type.EmptyTypes), new object[0]));
tb.AddInterfaceImplementation(typeof(IBasicRecord));
FieldBuilder[] fields = new FieldBuilder[names.Length];
var dataMemberCtor = typeof(DataMemberAttribute).GetConstructor(Type.EmptyTypes);
var dataMemberProps = new[] { typeof(DataMemberAttribute).GetProperty("Order") };
for (int i = 0; i < fields.Length; i++)
{
var field = fields[i] = tb.DefineField("_" + names[i],
types[i], FieldAttributes.Private);
var prop = tb.DefineProperty(names[i], PropertyAttributes.None,
types[i], Type.EmptyTypes);
var getter = tb.DefineMethod("get_" + names[i],
MethodAttributes.Public | MethodAttributes.HideBySig, types[i], Type.EmptyTypes);
prop.SetGetMethod(getter);
var il = getter.GetILGenerator();
il.Emit(OpCodes.Ldarg_0); // this
il.Emit(OpCodes.Ldfld, field); // .Foo
il.Emit(OpCodes.Ret); // return
var setter = tb.DefineMethod("set_" + names[i],
MethodAttributes.Public | MethodAttributes.HideBySig, typeof(void), new Type[] { types[i] });
prop.SetSetMethod(setter);
il = setter.GetILGenerator();
il.Emit(OpCodes.Ldarg_0); // this
il.Emit(OpCodes.Ldarg_1); // value
il.Emit(OpCodes.Stfld, field); // .Foo =
il.Emit(OpCodes.Ret);
prop.SetCustomAttribute(new CustomAttributeBuilder(
dataMemberCtor, new object[0],
dataMemberProps, new object[1] { i + 1 }));
}
foreach (var prop in typeof(IBasicRecord).GetProperties())
{
var accessor = prop.GetGetMethod();
if (accessor != null)
{
var args = accessor.GetParameters();
var argTypes = Array.ConvertAll(args, a => a.ParameterType);
var method = tb.DefineMethod(accessor.Name,
accessor.Attributes & ~MethodAttributes.Abstract,
accessor.CallingConvention, accessor.ReturnType, argTypes);
tb.DefineMethodOverride(method, accessor);
var il = method.GetILGenerator();
if (args.Length == 1 && argTypes[0] == typeof(int))
{
var branches = new Label[fields.Length];
for (int i = 0; i < fields.Length; i++)
{
branches[i] = il.DefineLabel();
}
il.Emit(OpCodes.Ldarg_1); // key
il.Emit(OpCodes.Switch, branches); // switch
// default:
il.ThrowException(typeof(ArgumentOutOfRangeException));
for (int i = 0; i < fields.Length; i++)
{
il.MarkLabel(branches[i]);
il.Emit(OpCodes.Ldarg_0); // this
il.Emit(OpCodes.Ldfld, fields[i]); // .Foo
if (types[i].IsValueType)
{
il.Emit(OpCodes.Box, types[i]); // (object)
}
il.Emit(OpCodes.Ret); // return
}
}
else
{
il.ThrowException(typeof(NotImplementedException));
}
}
accessor = prop.GetSetMethod();
if (accessor != null)
{
var args = accessor.GetParameters();
var argTypes = Array.ConvertAll(args, a => a.ParameterType);
var method = tb.DefineMethod(accessor.Name,
accessor.Attributes & ~MethodAttributes.Abstract,
accessor.CallingConvention, accessor.ReturnType, argTypes);
tb.DefineMethodOverride(method, accessor);
var il = method.GetILGenerator();
if (args.Length == 2 && argTypes[0] == typeof(int) && argTypes[1] == typeof(object))
{
var branches = new Label[fields.Length];
for (int i = 0; i < fields.Length; i++)
{
branches[i] = il.DefineLabel();
}
il.Emit(OpCodes.Ldarg_1); // key
il.Emit(OpCodes.Switch, branches); // switch
// default:
il.ThrowException(typeof(ArgumentOutOfRangeException));
for (int i = 0; i < fields.Length; i++)
{
il.MarkLabel(branches[i]);
il.Emit(OpCodes.Ldarg_0); // this
il.Emit(OpCodes.Ldarg_2); // value
il.Emit(types[i].IsValueType ? OpCodes.Unbox_Any : OpCodes.Castclass, types[i]); // (SomeType)
il.Emit(OpCodes.Stfld, fields[i]); // .Foo =
il.Emit(OpCodes.Ret); // return
}
}
else
{
il.ThrowException(typeof(NotImplementedException));
}
}
}
var type = tb.CreateType();
var obj = Activator.CreateInstance(type);
// we'll use the index (via a known interface) to set the values
IBasicRecord rec = (IBasicRecord)obj;
rec[0] = 123;
rec[1] = "abc";
rec[2] = 12F;
rec[3] = DateTime.Now;
for (int i = 0; i < 4; i++)
{
Console.WriteLine("{0} = {1}", i, rec[i]);
}
using (var ms = new MemoryStream())
{
var ser = new XmlSerializer(type);
ser.Serialize(ms, obj);
Console.WriteLine("XmlSerializer: {0} bytes", ms.Length);
}
using (var ms = new MemoryStream())
{
using (var writer = new StreamWriter(ms, Encoding.UTF8, 1024, true))
{
var ser = new JsonSerializer();
ser.Serialize(writer, obj);
}
Console.WriteLine("Json.NET: {0} bytes", ms.Length);
}
using (var ms = new MemoryStream())
{
var ser = new DataContractSerializer(type);
ser.WriteObject(ms, obj);
Console.WriteLine("DataContractSerializer: {0} bytes", ms.Length);
}
using (var ms = new MemoryStream())
{
Serializer.NonGeneric.Serialize(ms, obj);
Console.WriteLine("protobuf-net: {0} bytes", ms.Length);
}
using (var ms = new MemoryStream())
{
// note: NEVER do this unless you have a custom Binder; your
// assembly WILL NOT deserialize in the next AppDomain (i.e.
// the next time you load your app, you won't be able to load)
// - shown only for illustration
var bf = new BinaryFormatter();
bf.Serialize(ms, obj);
Console.WriteLine("BinaryFormatter: {0} bytes", ms.Length);
}
}
}
Output:
XmlSerializer: 246 bytes
Json.NET: 81 bytes
DataContractSerializer: 207 bytes
protobuf-net: 25 bytes
BinaryFormatter: 182 bytes

This is actually quite a complex question. Unfortunately, to answer it fully you would have to basically write it and test it, however - I strongly suggest not looking at any on-the-fly POCO generation until you have your answer! Basically, you should ignore that step for now.
The other essential question in performance is: how fast does it need to be? The absolute first thing I would do is the absolutely simplest thing that works, and measure that. And the simplest thing that works is: load it into a DataTable and serialize that datatable (using RemotingFormat = RemotingFormat.Binary;). In 10 lines of code that will give you a
line in the sand:
var dt = new DataTable();
dt.Load(yourDataReader);
//... any access tests
dt.RemotingFormat = SerializationFormat.Binary;
using (var file = File.Create(path))
{
var bf = new BinaryFormatter();
bf.Serialize(file, dt);
}
// ... also check deserialize, if that is perf-critical
Normally I wouldn't recommend either DataTable or BinaryFormatter, but... it doesn't seem far-fetched in this case.
Personally, I suspect you'll find that DataTable in binary-remoting-mode isn't actually terrible.
The next step is to see what else works without any huge effort. For example:
loading a data-source into objects is a solved problem, with tools like dapper
serializing a set of objects in a very efficient way is a solved problem, with tools like protobuf-net
So I would be tempted to create an illustrative class (purely to see if it is any better) along the lines of:
[DataContract]
public class Foo {
[DataMember(Order=1)] public int Id {get;set;}
[DataMember(Order=2)] public string Name {get;set;}
// ... more props
// IMPORTANT: make this representative - basically, the same data
// that you had in the data-table
// note also include any supporting info - any indexers and interface
// support that your core code needs
}
[DataContract]
public class FooWrapper { // just to help in the test
[DataMember(Order=1)] public List<Foo> Items {get;set;}
}
and do the same test (your main code would only use the indexer access, but let dapper use the .Query<Foo>(...) API for now):
var data = conn.Query<Foo>(...).ToList(); // dapper
//... any access tests, just using the indexer API
using (var file = File.Create(path))
{
var wrapper = new FooWrapper { Items = data };
Serializer.Serialize(file, wrapper); // protobuf-net
}
// note that you deserialize via Serializer.Deserialize<FooWrapper>(file)
The point of this is that this will give you some bounds on what is reasonable to expect in terms of what can be achieved. Feel free to use your own materializer/serializer in place of dapper/protobuf-net, but I humbly submit that these two have been heavily optimized for scenarios largely like this.
When you have a lower and upper bound, you have sensible data to answer the "is it worth it" question. Generating objects at run-time isn't massively hard, but it is more work than most people would need to do. You also want to be really careful to re-use the generated types as far as possible. Note that if you go that route, protobuf-net has a fully non-generic API, via Serializer.NonGeneric or RuntimeTypeModel.Default (all three options end up at the same core). Dapper doesn't, but I would be more than happy to add one (accepting a Type instance). In the interim, you could also use MakeGenericMethod / Invoke for that one step.
I realize I haven't directly answered "is it worth it", but that is deliberate: that cannot be answered without direct application to your scenario. Hopefully, I have instead provided some hints at how you can answer it for your scenario. I would be very interested in hearing your findings.
Only when you know that it is worth it (and with the above I would expect that to take about an hour's effort) would I go to the trouble of generating types. If you do, I recommend the use of Sigil - it will make your IL generation far less frustrating.

Dynamically calling a dll and method with arguments

Basically I'm trying to call a dll by name, instantiate an object, then call a method by name in that dll. I'm getting an "Exception has been thrown by the target of an invocation." during the Method.Invoke. I'm fairly sure my problem is with the typecasting of the arguments of the method. I was wondering if anyone had any input on this exception. Additionally, any suggestions on how to revise my approach are welcome.
public void calldll(string dllName, string typeName, string methodName, string arguments) {
string[] argumentArray = arguments.Split(new char[] { '|' }, StringSplitOptions.None);
Assembly assembly = Assembly.LoadFrom(dllName);
System.Type type = assembly.GetType(typeName);
Object o = Activator.CreateInstance(type);
MethodInfo method = type.GetMethod(methodName);
ParameterInfo[] parameters = method.GetParameters();
object[] methodParameters = new object[parameters.GetLength(0)];
for (int i = 0; i < parameters.Length - 1; i++)
{
var converter = TypeDescriptor.GetConverter(parameters[i].GetType());
methodParameters[i] = converter.ConvertFrom(argumentArray[i]);
}
method.Invoke(o, methodParameters); }

I found two issues with your code:
You are not looping over all parameters. You should remove -1 from the for loop.
When you are creating your converter, you call the GetType() method. This returns the Type of the ParameterInfo object, not the Type of the parameter. Use the property ParameterType instead.
All in all, change the first lines in the for loop to this:
for (int i = 0; i < parameters.Length; i++)
{
var converter = TypeDescriptor.GetConverter(parameters[i].ParameterType);
Once you have done these corrections, I believe your code should run as intended. At least it did for me when I tested a simple void Hello(int x, string y) method.

How do I make the type of a generic delegate in C#/.NET 4?

I can make the type of a delegate at runtime from a list of parameter System.Type, thanks to a answer to a question here.
But how do I do this when one of the parameters is a generic parameter, say it represents something like the following?
delegate t ScanFun<t>();
I want a System.Type which represents a generic delegate so I can call Type.MakeGenericType method with the type for the generic parameter t. However, I can't even find a way to find out what the type of that looks like.
The use is in a code analysis tool. This is the code I have which works with known types:
System.Type[] parms = new Type[f.sig.Parms.list.Length + 1];
specs[0] = f.sig.ReturnType.Type;
for (int i = 0; i < f.sig.Parms.list.Length; i++)
specs[i + 1] = f.sig.Parms.list[i].Type;
for (int i = 0; i < parmTypes_.Length; i++)
{
if (f.sig.Generic.List.Contains(specs[i].Name))
{
/// TODO: Make generic parameter Type here
goto done;
}
parms[i] = f.Parent.findType(specs[i]);
done: ;
}
var dtype = System.Linq.Expressions.Expression.GetDelegateType(parms);

Type openScanFunType = typeof(ScanFun<>);
Type closedScanFunType = openScanFunType.MakeGenericType(new[] { typeof(int) });
Alternatively (and this works better if there are multiple type parameters):
Type openScanFunType = typeof(ScanFun<string>).GetGenericTypeDefinition();
Type cloCsedScanFunType = openScanFunType.MakeGenericType(new[] { typeof(int) });

Instantiating a class using Reflection

Suppose I have three projects in my sln.
(1) xyz.a{Class Lib}{no reference added}
(2) yzx.b{Class Lib}{added the reference of xyz.a}
(3) zxy.c{Console App}{added the reference of xyz.a}
Now, I need to create the instance of a class residing in yzx.b from within xyz.a using reflection.
And also this should be independent of the folder/directory-names.
I.e. even If I change the name of the directory of yzx.b, it should work.
Does anyone have any idea?

First of all, Activator.CreateInstance() is a right way.
But, there is a more interesting way that is:
10 times faster
Don't wrap exceptions in
TargetInvocationException
Just create expression that calls constructor:
public static Func<object[], object> CreateConstructorDelegate(ConstructorInfo method)
{
var args = Expression.Parameter(typeof(object[]), "args");
var parameters = new List<Expression>();
var methodParameters = method.GetParameters().ToList();
for (var i = 0; i < methodParameters.Count; i++)
{
parameters.Add(Expression.Convert(
Expression.ArrayIndex(args, Expression.Constant(i)),
methodParameters[i].ParameterType));
}
var call = Expression.Convert(Expression.New(method, parameters), typeof(object));
Expression body = call;
var callExpression = Expression.Lambda<Func<object[], object>>(body, args);
var result = callExpression.Compile();
return result;
}
Performance test:
public void activator()
{
var stopwatch = new Stopwatch();
const int times = 10000000;
stopwatch.Start();
for (int i = 0; i < times; i++)
{
var v = Activator.CreateInstance(typeof (C));
}
stopwatch.Stop();
Console.WriteLine(stopwatch.ElapsedMilliseconds + "ms with activator");
var del = CreateConstructorDelegate(typeof(C).GetConstructor(new Type[0]));
stopwatch = new Stopwatch();
stopwatch.Start();
var args = new object[0];
for (int i = 0; i < times; i++)
{
var v = del(args);
}
stopwatch.Stop();
Console.WriteLine(stopwatch.ElapsedMilliseconds + "ms with expression");
}
Output:
1569ms with activator
134ms with expression
But:
C# 3.0 only
Complile() is long running operation
Just for curious.

You might want to check out the Activator.CreateInstance() methods. Just pass it the name of the assembly and type.
If you don't have a compile-time reference to the assembly, you can still reference it at runtime with Assembly.Load().

You can use Activator.CreateInstance to create an instance easily (this also does various caching of reflection information to make repeated calls faster), or Type.GetConstructor if you want to reflect over the constructor itself as well as directly running it (via ConstructorInfo.Invoke)