Is it possible to define a DynamicMethod with generic type parameters? The MethodBuilder class has the DefineGenericParameters method. Does the DynamicMethod have a counterpart? For example is it possible to create method with a signature like the one given blow using DynamicMethod?
void T Foo<T>(T a1, int a2)
This doesn't appear to be possible: as you've seen DynamicMethod has no DefineGenericParameters method, and it inherits MakeGenericMethod from its MethodInfo base class, which just throws NotSupportedException.
A couple of possibilities:
Define a whole dynamic assembly using AppDomain.DefineDynamicAssembly
Do generics yourself, by generating the same DynamicMethod once for each set of type arguments
Actually there is a way, it's not exactly generic but you'll get the idea:
public delegate T Foo<T>(T a1, int a2);
public class Dynamic<T>
{
public static readonly Foo<T> Foo = GenerateFoo<T>();
private static Foo<V> GenerateFoo<V>()
{
Type[] args = { typeof(V), typeof(int)};
DynamicMethod method =
new DynamicMethod("FooDynamic", typeof(V), args);
// emit it
return (Foo<V>)method.CreateDelegate(typeof(Foo<V>));
}
}
You can call it like this:
Dynamic<double>.Foo(1.0, 3);
Related
I want to create dynamic assembly with generic class:
class TestClass<T> where T : new() {
public T TestMethod() {
return f();
}
private Func<T> f;
}
So, I created class, added generic argument, set constraints and created delegate like this:
var fieldType = typeof(Func<>).MakeGenericType(TArg);
// TArg = testClassBuilder.DefineGenericParameters("T")[0];
Then using IL generator I tried to emit calling Invoke method:
ilGenerator.Emit(OpCodes.Callvirt, fieldType.GetMethod("Invoke"));
But I get NotSupportedException on GetMethod("Invoke") call. So, how to call this delegate using Emit?
You cannot call GetMethod on typeof(Func<>).MakeGenericType(TArg), because in this instance, TArg is a GenericTypeParameterBuilder, and the Type object returned by MakeGenericType doesn't know how to get the relevant methods.
Instead use TypeBuilder.GetMethod like this:
ilGenerator.Emit(
OpCodes.Callvirt,
TypeBuilder.GetMethod(
typeof(Func<>).MakeGenericType(genParam),
typeof(Func<>).GetMethod("Invoke")
));
I want to invoke a generic method having two different generic type parameters. Below is what my method looks like:
public class ABC<T> : IABC<T> where T: class,new()
{
public T Merge<T1>(T child, T parent, T1 rule){
}
}
I want to invoke the Merge method from another method. Below is what I have tried to invoke it.
Type mergerType = GetType().GetGenericTypeDefinition();
Type constructed = mergerType.MakeGenericType(new[]
{
childValue.GetType()
});
object mergerInstance = Activator.CreateInstance(constructed);
MethodInfo methodInfo = GetType().GetMethod("Merge");
MethodInfo method = methodInfo.MakeGenericMethod(ruleValue.GetType());
mergedObject = method.Invoke(mergerInstance, new[]
{
childValue,
parentValue,
ruleValue
});
While doing this I am getting a exception "object does not match target type" after method.invoke().
I cannot change the class or method definition of ABC class or Merge method because many other classes are implementing the IABC interface.
So can someone answer how can I invoke the Merge method.
You have to use the Merge method of the newly constructed type.
Change MethodInfo methodInfo = GetType().GetMethod("Merge");
to: MethodInfo methodInfo = constructed.GetMethod("Merge");
I need to call a generic method that takes a generic Func as one of its parameters, where the Type parameter is known only at runtime. This part of the code is an object mapper, which maps properties between a source and a target object. ViewModelBase is the root of classes that are considered "target" objects.
The method that I want to call (defined on ObjectMapperBuilder) has this signature:
public static ObjectMapperBuilder<TTarget> Create(
Type sourceType,
MappingDirection direction,
Func<TTarget, IDictionary<String, object>> getDictionaryFromTarget = null
);
In my base class, I want to call the above method, but use the most derived type as my type parameter:
public ViewModelBase {
private ConcurrentDictionary<string, object> _propertyValues;
public ViewModelBase (object sourceObject) {
Type tTarget = this.GetType();
// 1. How do I create the Func? All it does is return a private member.
// This is wrong because it uses a compile-time generic parameter.
Func<TTarget,IDictionary<String,object>> myFunc = (vm) => vm._propertyValues;
// 2. Ho do I call the Create method using reflection to specify the
// TTarget generic parameter at runtime?
var myMapper = ObjectMapperBuilder<TTarget>.Create(
sourceObject.GetType(),
MappingDirection.Bidirectional,
myFunc
);
// Do stuff with myMapper.
...
}
The purpose of this exercise is to be able to create the mapper in a method on the base class. The mapper must be created using the most derived type because I cache mappers according to source and target types, and different derived types need different mappers.
This might be a job for Expression trees and Activator, but I can't figure it out.
Part of the answer might be found in the answer to this question:
Runtime creation of generic Func<T>
This might be a simple answer, but could you make your view model base type generic, e.g.:
public class ViewModelBase<T> where T : ViewModelBase<T>
Allowing you to apply the inheritance:
public class SubViewModelBase: ViewModelBase<SubViewModelBase>
That way, your implementation would simply be:
Func<T, IDictionary<string, object>> props = (vm) => vm._propertyValues;
var mapper = ObjectMapperBuilder<T>.Create(
sourceObject.GetType(),
MappingDirection.Bidirectional,
props);
I settled on a solution with a compromise. I created a method "GetProperties" which does what I want, then wrap it in a delegate using Delegate.CreateDelegate.
protected static IDictionary<string, object> GetProperties(ViewModelBase viewModel)
{
return viewModel._propertyValues;
}
protected Delegate GetPropertiesFunc()
{
Type funcType = typeof(Func<,>).MakeGenericType(this.GetType(), typeof(IDictionary<String,object>));
MethodInfo method = typeof(ViewModelBase).GetMethod("GetProperties",
BindingFlags.NonPublic | BindingFlags.Static
);
return Delegate.CreateDelegate(funcType, method);
}
When I later need the Delegate as a particular Func, I call GetPropertiesFunc and pass it to Activator.CreateInstance, which works successfully.
Lets say I have a function
public void func1<T>();
And another function:
public void func2(Type type);
Inside func2, I want to call func1 with type. how can I "Convert" the type so it can fit in?
edit:
I didn't thought it will matter, but func1 is not my function. it part of the framework:
context.CreateObjectSet<T>()
You cannot call the generic function explicitly because you do not know the type at compile time. You can use reflections to call func1 and specify your type as generic argument. However I would advise you to change the signature of the methods to avoid using reflections if possible.
Here is an example of how to do it with Reflections:
private static void Method1(Type type)
{
MethodInfo methodInfo = typeof(Program).GetMethod("Method2", BindingFlags.NonPublic | BindingFlags.Static);
MethodInfo genericMethodInfo = methodInfo.MakeGenericMethod(type);
genericMethodInfo.Invoke(null, null);
}
private static void Method2<T>()
{
Console.WriteLine(typeof(T).FullName);
}
You would have to use reflection.
public void func2(Type type)
{
// call func1<T>()
var thisType = this.GetType();
var method = thisType.GetMethod("func1", new Type[0]).MakeGenericMethod(type);
method.Invoke(this, null);
}
Another option, of course: you can simply go the other direction and make the Type version the "real" one:
public T func1<T>()
{
func2(typeof(T));
}
public object func2(Type type)
{
Console.WriteLine(type.FullName);
}
This is similar to how the framework implements Enum.TryParse<TEnum> and Enum.TryParseEnum. The implementation of the generic TEnum variant simply passes it along (via typeof(TEnum)) to the non-generic (Type-based) method.
I was hoping to do something like this, but it appears to be illegal in C#:
public Collection MethodThatFetchesSomething<T>()
where T : SomeBaseClass
{
return T.StaticMethodOnSomeBaseClassThatReturnsCollection();
}
I get a compile-time error:
'T' is a 'type parameter', which is not valid in the given context.
Given a generic type parameter, how can I call a static method on the generic class? The static method has to be available, given the constraint.
In this case you should just call the static method on the constrainted type directly. C# (and the CLR) do not support virtual static methods. So:
T.StaticMethodOnSomeBaseClassThatReturnsCollection
...can be no different than:
SomeBaseClass.StaticMethodOnSomeBaseClassThatReturnsCollection
Going through the generic type parameter is an unneeded indirection and hence not supported.
To elaborate on a previous answer, I think reflection is closer to what you want here. I could give 1001 reasons why you should or should not do something, I'll just answer your question as asked. I think you should call the GetMethod method on the type of the generic parameter and go from there. For example, for a function:
public void doSomething<T>() where T : someParent
{
List<T> items=(List<T>)typeof(T).GetMethod("fetchAll").Invoke(null,new object[]{});
//do something with items
}
Where T is any class that has the static method fetchAll().
Yes, I'm aware this is horrifically slow and may crash if someParent doesn't force all of its child classes to implement fetchAll but it answers the question as asked.
You can do what I call a surrogate singleton, I've been using it as a sort of "static inheritance" for a while
interface IFoo<T> where T : IFoo<T>, new()
{
ICollection<T> ReturnsCollection();
}
static class Foo<T> where T : IFoo<T>, new()
{
private static readonly T value = new();
public static ICollection<T> ReturnsCollection() => value.ReturnsCollection();
}
// Use case
public ICollection<T> DoSomething<T>() where T : IFoo<T>, new()
{
return Foo<T>.ReturnsCollection();
}
The only way of calling such a method would be via reflection, However, it sounds like it might be possible to wrap that functionality in an interface and use an instance-based IoC / factory / etc pattern.
It sounds like you're trying to use generics to work around the fact that there are no "virtual static methods" in C#.
Unfortunately, that's not gonna work.
I just wanted to throw it out there that sometimes delegates solve these problems, depending on context.
If you need to call the static method as some kind of a factory or initialization method, then you could declare a delegate and pass the static method to the relevant generic factory or whatever it is that needs this "generic class with this static method".
For example:
class Factory<TProduct> where TProduct : new()
{
public delegate void ProductInitializationMethod(TProduct newProduct);
private ProductInitializationMethod m_ProductInitializationMethod;
public Factory(ProductInitializationMethod p_ProductInitializationMethod)
{
m_ProductInitializationMethod = p_ProductInitializationMethod;
}
public TProduct CreateProduct()
{
var prod = new TProduct();
m_ProductInitializationMethod(prod);
return prod;
}
}
class ProductA
{
public static void InitializeProduct(ProductA newProduct)
{
// .. Do something with a new ProductA
}
}
class ProductB
{
public static void InitializeProduct(ProductB newProduct)
{
// .. Do something with a new ProductA
}
}
class GenericAndDelegateTest
{
public static void Main()
{
var factoryA = new Factory<ProductA>(ProductA.InitializeProduct);
var factoryB = new Factory<ProductB>(ProductB.InitializeProduct);
ProductA prodA = factoryA.CreateProduct();
ProductB prodB = factoryB.CreateProduct();
}
}
Unfortunately you can't enforce that the class has the right method, but you can at least compile-time-enforce that the resulting factory method has everything it expects (i.e an initialization method with exactly the right signature). This is better than a run time reflection exception.
This approach also has some benefits, i.e you can reuse init methods, have them be instance methods, etc.
You should be able to do this using reflection, as is described here
Due to link being dead, I found the relevant details in the wayback machine:
Assume you have a class with a static generic method:
class ClassWithGenericStaticMethod
{
public static void PrintName<T>(string prefix) where T : class
{
Console.WriteLine(prefix + " " + typeof(T).FullName);
}
}
How can you invoke this method using relection?
It turns out to be very easy… This is how you Invoke a Static Generic
Method using Reflection:
// Grabbing the type that has the static generic method
Type typeofClassWithGenericStaticMethod = typeof(ClassWithGenericStaticMethod);
// Grabbing the specific static method
MethodInfo methodInfo = typeofClassWithGenericStaticMethod.GetMethod("PrintName", System.Reflection.BindingFlags.Static | BindingFlags.Public);
// Binding the method info to generic arguments
Type[] genericArguments = new Type[] { typeof(Program) };
MethodInfo genericMethodInfo = methodInfo.MakeGenericMethod(genericArguments);
// Simply invoking the method and passing parameters
// The null parameter is the object to call the method from. Since the method is
// static, pass null.
object returnValue = genericMethodInfo.Invoke(null, new object[] { "hello" });
As of now, you can't. You need a way of telling the compiler that T has that method, and presently, there's no way to do that. (Many are pushing Microsoft to expand what can be specified in a generic constraint, so maybe this will be possible in the future).
Here, i post an example that work, it's a workaround
public interface eInterface {
void MethodOnSomeBaseClassThatReturnsCollection();
}
public T:SomeBaseClass, eInterface {
public void MethodOnSomeBaseClassThatReturnsCollection()
{ StaticMethodOnSomeBaseClassThatReturnsCollection() }
}
public Collection MethodThatFetchesSomething<T>() where T : SomeBaseClass, eInterface
{
return ((eInterface)(new T()).StaticMethodOnSomeBaseClassThatReturnsCollection();
}