Develop Reference

Can I take a method identifier (ex: MyClass.MyMethod) as a method parameter in C#?

The way nameof() works, I can write
var s = nameof(HomeController.Index);
Can I make my own compile-time method that works the same way and can take the same input? For example:
public static string MyMethod(Something input) // I'm not sure what Something should be
{
// do something with input to get method info
}
... // elsewhere in code
var s = MyMethod(HomeController.Index);
Update for context:
More specifically I would like to be able to make a helper method to be used in a Razor view. For example, I might call MyMethod(HomeController.Index) to return a string listing the controller name and the action name. It would be nice to be able to make such a method without having to pass both the controller type HomeController and the method name Invoke as separate parameters.
Update for more context and example:
My goal is to avoid magic strings when specifying controllers and actions in Razor views. Here's an example of how I am doing this currently by checking for the [Action] attribute on actions and trimming of the "Controller" suffix from controllers. But you can see that it's verbose.
<a asp-action="#(ControllerHelpers.GetActionName<HomeController>(nameof(HomeController.Index)))" asp-controller="#(ControllerHelpers.GetRouteName<HomeController>())">Link to Home</a>
I'm looking for a way to do something like this
<a asp-action="#ControllerHelpers.GetActionName(HomeController.Index)" asp-controller="#(ControllerHelpers.GetRouteName<HomeController>())">Link to Home</a>
and perhaps eventually my own tag helper like this. But even here I'd like to avoid having to separately pass both the controller and the action name (just for concision).
<a asp-controller-action="HomeController.Index">Link to Home</a>

You can do this via reflection, passing the method name as a string, and then using Type.GetMethod to get the method and then call Invoke on that, with the type instance.
However, the better thing to do here is to use a delegate. Specifically, you can do something like:
public static string MyMethod(Func<IActionResult> func)
And then:
var s = MyMethod(() => controller.Index());
Inside MyMethod, you'd invoke this like any other method, i.e. func().
That said, what you're trying to ultimately achieve here is unclear and suspect. You can't just invoke HomeController.Index; you need a HomeController instance. Manually newing up a controller, is pretty much always wrong, so there's probably a better way to achieve what you want, in general.
In other words, you seem to have an XY problem here. You're trying to do X, and you've decided Y is the way to do that (here, trying to pass a method reference and invoke that for some reason). But, you don't know how to do Y, either. Instead of asking about X, i.e. the thing you actually need help with, you're asking about Y, which almost assuredly isn't even a good way to do X, in the first place. Give us some more info on X, the thing you actually want, and we can probably give you a better method to achieve that.

I'm not 100% sure what you're asking for, but here's an example of how to do something like what you're asking for using delegates (MS delegate guide):
class MethodRunner
{
// use delegates to define the method signature that you'll operate on
public delegate void NoArgFormat();
public delegate void OneStringArgFormat(String arg);
//You can accept delegates as function arguments, then call them
//with a "live" object instance
public void RunMyMehtod(NoArgFormat methodToRun)
{
methodToRun();//runs the methd passed in
}
public void RunMyStringArgMethod(OneStringArgFormat methodToRun, String arg)
{
methodToRun(arg);
}
}
class Program
{
//This matches to "NoArgFormat" delegate definition
public void Method1()
{
Console.WriteLine("Method1");
}
//This matches the OneStringArgFormat
public void Method2(String arg)
{
Console.WriteLine(arg);
}
static void Main(string[] args)
{
Program p = new Program();
MethodRunner mr = new MethodRunner();
mr.RunMyMehtod(p.Method1);
mr.RunMyStringArgMethod(p.Method2, "First");
mr.RunMyStringArgMethod(p.Method2, "Second");
}
}
Sample output:
C:\Workspace\SampleApp\bin\Debug>SampleApp.exe
Method1
First
Second

Using methods from a type passed as a parameter in C#

I'm working in Q#, a quantum programming language based on C#. Quantum operations become C# classes, from which you can do things like
QuantumOperation.run(simulator, param1, param2);
which will use a quantum simulator simulator to run the operation QuantumOperation with the parameters param1 and param2.
I have many different operations which I want to run using different simulators and different parameters. What I would like to do is pass the quantum operation to another method, which will iterate through all the simulators and parameters. Then I can call this method with all the quantum operations I want.
The problem is that - as far as I can tell - a quantum operation is really a class and not an object. So, for example, if I write:
static void someMethod<Qop>(){...}
then I can call this with a quantum operation QuantumOperation as:
someMethod<QuantumOperation>()
and it compiles fine. However, if I try to do something like
static void someMethod<Qop>(Qop quantumOperation){ ...}
someMethod<QuantumOperation>(quantumOperation);
I get an error of "QuantumOperation is a type, which is not valid in the given context" for the second line.
If I try:
static void someMethod<Qop>(...){
...
Qop.Run(...);
...
}
it similarly says: "'Qop' is a type parameter, which is not valid in the given context".
What seems to be happening here is that I'm passing the class as a type. But then when I want to treat the type as a class, I can't. I looked for ways to pass a class as an argument, but I only see ways to do this that will create objects in that class. But I can't use an object, since "Run" is a static method.
(I could try passing an object and getting the class from that, but (a) I don't know if it's possible to create objects of quantum operation classes, and (b) I can only find public Type GetType, which returns a type and not a class, giving the same problem).
Is there any way to pass a class as an argument, then reference static methods of that class, without ever instantiating an object?
Now, maybe I'm asking too much, since, as far as C# is concerned, it's a coincidence that all these classes have a method called "Run". It maybe shouldn't be able to attempt to call methods with the same name from different classes.
Alternatively, I could construct a method for each quantum operation and then pass those methods. The method would look like:
static void QuantumOperationWrapper(QuantumSimulator simulator, Int int_parameter){
QuantumOperation.Run(simulator, in_parameter);
}
I would need to make a new method for each quantum operation, but that's not that bad. Then I can pass this as a delegate or Func to the methods I want. The problem is that the results I want are contained in the QuantumSimulator object. So what I want to do is something like:
QuantumOperationWrapper(simulator, 3);
simulator.GetResults();
But when I do this, the results are empty. My guess is that, somehow, the simulator is being passed by value, or treated as immutable, or something that prevents QuantumOperationWrapper from altering internal parameters of the simulator.
Is there any way to I can ensure that a delegate/Func will alter the internal state of its arguments?
EDIT: I can make a delegate for the Run method, as follows:
public delegate System.Threading.Tasks.Task<Microsoft.Quantum.Simulation.Core.QVoid> RunQop(QCTraceSimulator sim, long n);
Then I can construct static void someMethod(RunQop runner, ...), and pass QuantumOperation.Run as the first argument.
However, I have the same problem, that the QCTraceSimulator I pass as an argument does not keep any of the simulation results it makes when I call this.

So if I understand you correctly you want to execute a bunch of methods with parameters on different simulators. Here is how to do this:
We first off need a List of the operations we want to perform.
var methodList = new List<Func<QCTraceSimulator, long, Task<QVoid>>>
{
QuantumOperation.Run,
// Add more methods here
}
This is a List of Funcs. A Func is a delegate type that represents a method with a parameter and a return value. Here our methods need to look like this to be able to be added to our List:
public Task<QVoid> SomeName(QCTraceSimulator sim, long parameter)
{ ...}
We also need a list of parameters you want to try this with:
var paramsList = new List<long>
{
1,
2,
-2147483648,
2147483647
};
Now we can iterate through these and run our method like so:
public void RunMethodsOnSimulator(QCTraceSimulator sim)
{
// Iterate through every method
foreach (var method in methodList)
{
// Iterate through every parameter
foreach (var parameter in paramsList)
{
// Execute the given method with the given parameter
Task<QVoid> result = method(sim, parameter);
}
}
}
You can now do whatever you want with the result. This will result in every method being called with every parameter once
Please keep in mind that this answer only solves this problem for methods that return a Task<QVoid> and take a QCTraceSimulator and a long as parameter. This solution however avoids having to modify any QuantumOperation classes (and hopefully teaches you a little about delegates)
Here is what the paramsList and the RunMethodsOnSimulator method would like with 2 or more parameters:
methodList = new List<Func<QCTraceSimulator, long, int, Task<QVoid>>>
{
QuantumOperation.Run,
// Add more methods here
}
paramsList = new List<Tuple<long, int>>
{
new Tuple<long, int>(1, 1),
new Tuple<long, int>(2, 1),
new Tuple<long, int>(1, 2),
new Tuple<long, int>(-2147483648, 1)
}
public void RunMethodsOnSimulator(QCTraceSimulator sim)
{
// Iterate through every method
foreach (var method in methodList)
{
// Iterate through every parameter
foreach (var parameter in paramsList)
{
// Execute the given method with the given parameter
Task<QVoid> result = method(sim, parameter.Item1, parameter.Item2);
}
}
}

The way the Q# simulation tests deal with this is by having a method that receives a delegate with some code you want to execute on the simulator, in particular, the simulator unittests have the RunWithMultipleSimulators method that is broadly used in places like CoreTests.cs; this is an example of how it is used:
[Fact]
public void RandomOperation()
{
Helper.RunWithMultipleSimulators((s) =>
{
Circuits.RandomOperationTest.Run(s).Wait(); // Throws if it doesn't succeed
});
}

I think you're having two separate problems: you're not getting the results back, and dealing with classes is making looping through different operations difficult. Let me try to address them separately.
Results from running an operation are returned from the Run method, not stored in the simulator. More specifically, if you invoke an operation that returns a Q# int, the return value of the Run method will be Task<long>. You can then use the value property of the task to get the actual result, or use the async/await pattern, whichever you like.
All of the operation classes can be instantiated, and they all implement the ICallable interface. This interface has an Apply method that gets passed the arguments to the operation and returns the (asynchronous) results. Each instance has to get properly instantiated with a reference to the simulator; the easiest way to do this is to call the Get generic method on the simulator instance.
If you look at SimulatorBase.cs, in the implementation of the Run method on line 101, you can see how this is done. In this method, T is the class of the operation; I is the class of the operation input; and O is the class of the operation return value. You could use basically the same code to create a list of objects that you then call Apply on with varying arguments.

I did not understand everything but from the little that I understood you can use a non static wrapper and each wrapper allows accessing to a distinct Qop static class.
static public void TestQop()
{
someMethod(new Qop1(), 0, 0, 0);
someMethod(new Qop2(), 1, 1, 1);
}
static void someMethod<T>(T qop, int simulator, int param1, int param2)
where T : QopBase
{
qop.Run(simulator, param1, param2);
}
abstract class QopBase
{
public abstract void Run(int simulator, int param1, int param2);
}
class Qop1 : QopBase
{
public override void Run(int simulator, int param1, int param2)
{
QuantumOperation1.Run(simulator, param1, param2);
}
}
class Qop2 : QopBase
{
public override void Run(int simulator, int param1, int param2)
{
QuantumOperation2.Run(simulator, param1, param2);
}
}

Calling a method on an object whose type is generically defined requires you to use a generic constraint which ensures that the used generic type defines the expected method.
At its core, this relies on polymorphism to ensure that even though the specific type can vary, it is known that all usable generic types (which can be limited via constraints) contain this specific method you wish to call.
Static classes and methods lack this feature. They cannot inherit, nor can they implement interfaces, nor can you pass them via method parameters (and trying to do it via generic is not the solution). There is no way to create an "inheritance-like" link between two static methods of two different static classes; even if the methods have the same signature otherwise.
Are there other ways? Yes. In order of preferability:
(1) The straightforward and clean solution is avoiding statics and instead use instanced classes. If you are able to do this, this is the superior option.
(2) If you can't avoid statics, you can still wrap your static in an instanced wrapper, e.g.:
public class IWrapper
{
void DoTheThing(int foo);
}
public QuantumOperationWrapper : IWrapper
{
public void DoTheThing(int foo)
{
QuantumOperationWrapper.Run(foo);
}
}
public OtherStaticOperationWrapper : IWrapper
{
public void DoTheThing(int foo)
{
OtherStaticOperationWrapper.Run(foo);
}
}
This effectively "unstatics" the static code, in a way that you can now rely on the knowledge that all your wrappers implement/inherit the common BaseWrapper and thus both implement the DoTheThing method.
Your generic method can then rely on this:
public void DoTheGenericThing<T>(T obj) where T : IWrapper
{
obj.DoTheThing(123);
}
Note: In this particular case you don't even need generics to begin with. I assume you don't really need generics in this case, but since the answer can apply to both generic and non-generic cases, I've left the generic parameter in the solution. There may be specific cases in which you still need to use generics, though I suspect this is not one of them.
(3) A third but very dirty option is to use reflection to call the method anyway and just assume you never pass in a type which does not have the expected static method. But this is a really bad practice approach which will be fraught with bugs, it will be nigh impossible to debug, and it's absolutely not refactor-friendly.

Maybe you can try to deal with the situation using Interfaces. Something like that:
public interface IQuantumOperation
{
void Run();
void Run(MyFancyClazz simulator, MyFancyParam param1, MyFancyParam param2);
//And other possible methods
}
Then you can make use of this Interface as a type parameter's contract
static void someMethod<Qop>(Qop myQopParameter) where Qop : IQuantumOperation
{
...
//Now you can call your Run method
myQopParameter.Run(...);
...
//Or other fancy Run method with parameters like below
myQopParameter.Run(simulator, param1, param2);
}
Finally make sure that your QuantumOperation class implements the IQuantumOperation interface

How to use C# attributes to select a method in a class based on a string?

Suppose I have a class like this:
public class MyMethods
{
[SpecialMethod("test")]
public string GetTestString(int i)
{
return string.Format("Hello world {0} times!",i);
}
[SpecialMethod("lorem")]
public string GetSomeLoremIpsumText(int i)
{
// ignores the 'i' variable
return "Lorem ipsum dolor sit amet";
}
// ... more methods with the same signature here ...
public string DefaultMethod(int i)
{
return "The default method happened! The attribute wasn't found.";
}
public string ThisMethodShouldNotShowUpViaAttributes(int i)
{
return "You should not be here.";
}
}
I also have defined the attribute simply like this:
[AttributeUsage(AttributeTargets.Method)]
public class SpecialMethodAttribute : System.Attribute
{
private string _accessor;
public string Accessor
{
get
{
return _accessor;
}
}
public SpecialMethodAttribute(string accessor)
{
_accessor = accessor;
}
}
What I want to be able to do might look like this:
public class MethodAccessViaAttribute
{
private MyMethods _m;
public MethodAccessViaAttribute()
{
_m = new MyMethods();
}
public string CallMethodByAccessor(string accessor, int i)
{
// this is pseudo-code, expressing what I want to be able to do.
Func<int, string> methodToCall = FindAMethodByAttribute(_m, accessor);
if (methodToCall == null)
return _m.DefaultMethod(i);
else
return methodToCall(i);
}
public void Test()
{
// should print "Hello world 3 times!"
Console.WriteLine(CallMethodByAccessor("test",3));
// should print "Lorem ipsum dolor sit amet"
Console.WriteLine(CallMethodByAccessor("lorem",int.MaxValue));
// should print "The default method happened! The attribute wasn't found."
Console.WriteLine(CallMethodByAccessor("I-do-not-exist",0));
}
}
Notice that all methods using the SpecialMethod attribute follow the same method signature. Ideally, the search function would exclude methods not matching the signature, since a try/catch could be used to test if the method matches the Func signature.
Can I get a point in the right direction for how to accomplish this?

I don't like giving "do this instead" answers, but I can't put this inside a comment.
Instead of this, along with all of the supporting code to handle the attributes
public void Test()
{
Console.WriteLine(CallMethodByAccessor("test",3));
Console.WriteLine(CallMethodByAccessor("lorem",int.MaxValue));
Console.WriteLine(CallMethodByAccessor("I-do-not-exist",0));
}
This code does the exact same thing:
public void Test()
{
var methods = new MyMethods();
Console.WriteLine(methods.GetTestString("test", 3));
Console.WriteLine(methods.GetSomeLoremIpsumText("lorem", int.MaxValue));
}
The language is designed on purpose so that if a method doesn't exist, you can't call it. That helps us avoid mistakes at runtime. We don't want our application to execute something or ignore it based on whether or not we spelled a method name correctly. Someone could pull their hair out for hours trying to figure out why the application isn't working and then realize that it's because they misspelled "lorem." Just calling methods the "normal" way prevents all of that. If you misspell a method name then Visual Studio will show an error, the code won't compile, and it's super easy to find and fix. (Plus Intellisense/autocomplete will even help us see the methods that are available.)
Also, if you right-click on a method then Visual Studio will take you right to that method. With the string attributes someone has to follow a lot more code just to figure out which method is actually getting called. And if they need to debug and step through it, they need to step through all that extra stuff.
It's extremely common to have a bunch of classes that each implement the same interface and each have one method. It's good design to have fewer methods - even one - in an interface. (See Interface Segregation Principle.) No one will consider that "ugly." But if we invent our own way of doing it we can really confuse other developers who work on the same code, and it can be challenging to maintain even for the person who wrote it.

So I did figure out how to accomplish this task.
I created a class which all classes that contain methods will inherit from. I then created a private method which actually extract and create Func objects.
We need a method which will search for any method that has the desired attribute. Reflection has a MethodInfo class which represents a method. We can use some LINQ to search all of the methods on the class. We then use a little expression tree fun to generate the Func object that will actually call the method on this specific instance of the class:
// Locates a method on this class that has the SpecialMethod attribute of the given name
private Func<int, string> FindMethodByAccessor(string accessor)
{
// Find all methods containing the attribute
var desiredMethod = this.GetType().GetMethods()
.Where(x => x.GetCustomAttributes(typeof(SpecialMethod), false).Length > 0)
.Where(y => (y.GetCustomAttributes(typeof(SpecialMethod), false).First() as SpecialMethod).Accessor == accessor)
.FirstOrDefault();
if (desiredMethod == null) return null;
// This parameter is the first parameter passed into the method. In this case it is an int.
ParameterExpression x = Expression.Parameter(typeof(int));
// This parameter refers to the instance of the class.
ConstantExpression instance = Expression.Constant(this);
// This generates a piece of code and returns it in a Func object. We effectively are simply calling the method.
return Expression.Lambda<Func<int, string>>(
Expression.Call(instance, desiredMethod, new Expression[] { x }), x).Compile();
}
The idea of expression trees is still new to me, but this function does exactly what I want - it will locate a method on the instance of the class it's running in which has been decorated with the given attribute and return it as a Func object.
We can now finish the method which actually calls the other methods:
public string CallMethodByAccessor(string accessor, int i)
{
Func<int, string> methodToCall = FindMethodByAccessor(accessor);
if (methodToCall == null)
return DefaultMethod(i);
else
return methodToCall(i);
}
public string DefaultMethod(int i) { return "Unknown method requested!"; }
I still have not added checking to see whether the method with the attribute matches the necessary signature, but that could easily be done by working with properties on the MethodInfo object.
Finally, we wrap all this up in a class, which any other class can inherit from. The subclass then implements methods following the signature and decorates them with the attribute. To call the desired method by name, you simply call CallMethodByAccessor.
To respond finally to all of the suggestions to use a different methodology, I respect all of your ideas and, if the use case were different, this would absolutely be overkill and unnecessary. The specific use case at hand involves a Web service which users and developers can configure. The Web service lets a user specify one or more "endpoints". The endpoint in this case is merely a string. The library I am writing receives data from the Web service, and one of the parameters is the desired "endpoint" string. The idea is that the user could write endpoints as methods, give them any function name they desire, and then associate them with the actual endpoint text via the attribute. For example:
[Endpoint("user.login")]
public string performLogin(string credentialString)
{
// ...
}
Since the endpoint name is user.login we cannot simply name a class method with that name. Additionally, even if we did, we would still need to use reflection to dig into the class, extract the correct method, and generate a Func object to call the method. So, in this instance, using attributes simply makes development far easier, because the only alternative would be using a switch/case block that would have to be rigorously maintained. I feel it would be far more easy for a developer to "forget" to add another case block, or to forget to remove a case block which is no longer needed, than it would be to mess up the attributes. The attribute "ties" the endpoint name to the method, rather than having to keep track of both the method name and the endpoint name in a totally different block of code.
Finally, the "default" method is absolutely useful in this case. If a user instructs the Web service to call an endpoint which doesn't exist, the app can return a sensible response, e.g. "The endpoint 'MyEendpoint' does not exist." This would be much easier to debug than simply seeing the API crash!

Defining a delegate blueprint

I was reading this question where one answered suggests this method:
public static void Method<T>(Func<int,T> del) {
var t = del(42);
}
Which should be used like so: Method<SomeType>(x => new SomeType(x));
The Method body is not important to this question.
If the delegate/lambda is not in that "style", the method will not work as expected. For example, if it is called like Method(x => new Foo()); it will not "work" because the purpose of the workaround will be lost.
The purpose is ensuring that T has a constructor taking 1 parameter of type int. I wish I could do T(int)
So is there anyway to ensure that the delegate should always be be x => new SomeType(x)? Or is there any alternative? I have looked up a lot of places and can't come up with anything.

You don't need a func to do this. Just pass in the type you want and it will return the object and ensure the int gets passed into it. You're then basically just creating a factory method that will give you the type you want with the integer passed in.
public T Method<T>(int whatever) where T : class
{
return (T)Activator.CreateInstance(typeof(T), whatever);
}
var type = Method<SomeType>(55);

How to get the methodname from a known method?

Is it possible to get the name of another method in the same class but without using a manually written string?
class MyClass {
private void doThis()
{
// Wanted something like this
print(otherMethod.name.ToString());
}
private void otherMethod()
{
}
}
You may ask why: well the reason is that I must invoke the method later on like this Invoke("otherMethod"), however I don't want to hardcode this string myself as I can't refactor it anymore within the project.

One approach is you can wrap it into delegate Action, then you can access the name of method:
string name = new Action(otherMethod).Method.Name;

You can use reflection (example - http://www.csharp-examples.net/get-method-names/) to get the method names. You can then look for the method that you're looking for by name, parameters or even use an attribute to tag it.
But the real question is - are you sure this is what you need? This looks as if you don't really need reflection, but need to think over your design. If you already know what method you're going to invoke, why do you need the name? How about a using a delegate? Or exposing the method via an interface and storing a reference to some class implementing it?

Try this:
MethodInfo method = this.GetType().GetMethod("otherMethod");
object result = method.Invoke(this, new object[] { });

Btw. I also found (in the expansions of the internet) an alternative solution for only getting the string of a method. It also works with parameters and return types:
System.Func<float, string> sysFunc = this.MyFunction;
string s = sysFunc.Method.Name; // prints "MyFunction"
public string MyFunction(float number)
{
return "hello world";
}