I have to call a method whose name is coming from a configuration file. I can achieve this using Reflection.MethodInfo.Invoke() method. But my scenario is all these methods should be of same signature. Can i implement it using Delegates? but how can i add a method name stored in configuration file to a delegate?
Look at Delegate.CreateDelegate on MSDN. Some of the best docs there!
You can create a re-usable delegate if you wanted to, e.g. given my type:
public class MyClass
{
public void DoSomething(string argument1, int argument2)
{
Console.WriteLine(argument1);
Console.WriteLine(argument2);
}
}
I could do something like:
Action<object, MethodInfo, string, int> action =
(obj, m, arg1, arg2) => m.Invoke(obj, new object[] { arg1, arg2 });
And call it as:
var method = typeof(MyClass).GetMethod("DoSomething");
var instance = new MyClass();
action(instance, method, "Hello", 24);
If you know your method has a return type, you can do that with a System.Func delegate:
public class MyClass
{
public string DoSomething(string argument1, int argument2)
{
return string.Format("{0} {1}", argument1, argument2);
}
}
Func<object, MethodInfo, string, int, string> func =
(obj, m, arg1, arg2) => (string)m.Invoke(obj, new object[] { arg1, arg2 });
string result = func(instance, method, "Hello", 24);
Related
How do I create a Dictionary where I can store functions?
Thanks.
I have about 30+ functions which can be executed from the user. I want to be able to execute the function this way:
private void functionName(arg1, arg2, arg3)
{
// code
}
dictionaryName.add("doSomething", functionName);
private void interceptCommand(string command)
{
foreach ( var cmd in dictionaryName )
{
if ( cmd.Key.Equals(command) )
{
cmd.Value.Invoke();
}
}
}
However, the function signature is not always the same, thus having different amount of arguments.
Like this:
Dictionary<int, Func<string, bool>>
This allows you to store functions that take a string parameter and return boolean.
dico[5] = foo => foo == "Bar";
Or if the function is not anonymous:
dico[5] = Foo;
where Foo is defined like this:
public bool Foo(string bar)
{
...
}
UPDATE:
After seeing your update it seems that you don't know in advance the signature of the function you would like to invoke. In .NET in order to invoke a function you need to pass all the arguments and if you don't know what the arguments are going to be the only way to achieve this is through reflection.
And here's another alternative:
class Program
{
static void Main()
{
// store
var dico = new Dictionary<int, Delegate>();
dico[1] = new Func<int, int, int>(Func1);
dico[2] = new Func<int, int, int, int>(Func2);
// and later invoke
var res = dico[1].DynamicInvoke(1, 2);
Console.WriteLine(res);
var res2 = dico[2].DynamicInvoke(1, 2, 3);
Console.WriteLine(res2);
}
public static int Func1(int arg1, int arg2)
{
return arg1 + arg2;
}
public static int Func2(int arg1, int arg2, int arg3)
{
return arg1 + arg2 + arg3;
}
}
With this approach you still need to know the number and type of parameters that need to be passed to each function at the corresponding index of the dictionary or you will get runtime error. And if your functions doesn't have return values use System.Action<> instead of System.Func<>.
However, the function signature is not
always the same, thus having different
amount of arguments.
Let's start with a few functions defined like this:
private object Function1() { return null; }
private object Function2(object arg1) { return null; }
private object Function3(object arg1, object arg3) { return null; }
You really have 2 viable options at your disposal:
1) Maintain type-safety by having clients call your function directly.
This is probably the best solution, unless you have very good reasons for breaking from this model.
When you talk about wanting to intercept function calls, it sounds to me like you're trying to re-invent virtual functions. There's a boat load of ways to get this sort of functionality out of the box, such as inheriting from a base class an overriding its functions.
It sounds to me like you want a class that's more of a wrapper than a derived instance of a base class, so do something like this:
public interface IMyObject
{
object Function1();
object Function2(object arg1);
object Function3(object arg1, object arg2);
}
class MyObject : IMyObject
{
public object Function1() { return null; }
public object Function2(object arg1) { return null; }
public object Function3(object arg1, object arg2) { return null; }
}
class MyObjectInterceptor : IMyObject
{
readonly IMyObject MyObject;
public MyObjectInterceptor()
: this(new MyObject())
{
}
public MyObjectInterceptor(IMyObject myObject)
{
MyObject = myObject;
}
public object Function1()
{
Console.WriteLine("Intercepted Function1");
return MyObject.Function1();
}
public object Function2(object arg1)
{
Console.WriteLine("Intercepted Function2");
return MyObject.Function2(arg1);
}
public object Function3(object arg1, object arg2)
{
Console.WriteLine("Intercepted Function3");
return MyObject.Function3(arg1, arg2);
}
}
2) OR map the input of your functions to a common interface.
This might work if all of your functions are related. For example, if you're writing a game, and all the functions do something to some part of the player or player's inventory. You'd end up with something like this:
class Interceptor
{
private object function1() { return null; }
private object function2(object arg1) { return null; }
private object function3(object arg1, object arg3) { return null; }
Dictionary<string, Func<State, object>> functions;
public Interceptor()
{
functions = new Dictionary<string, Func<State, object>>();
functions.Add("function1", state => function1());
functions.Add("function2", state => function2(state.arg1, state.arg2));
functions.Add("function3", state => function3(state.arg1, state.are2, state.arg3));
}
public object Invoke(string key, object state)
{
Func<object, object> func = functions[key];
return func(state);
}
}
Define the dictionary and add the function reference as the value, using System.Action as the type:
using System.Collections;
using System.Collections.Generic;
public class Actions {
public Dictionary<string, System.Action> myActions = new Dictionary<string, System.Action>();
public Actions() {
myActions ["myKey"] = TheFunction;
}
public void TheFunction() {
// your logic here
}
}
Then invoke it with:
Actions.myActions["myKey"]();
Hey, I hope this helps. What language are you coming from?
internal class ForExample
{
void DoItLikeThis()
{
var provider = new StringMethodProvider();
provider.Register("doSomethingAndGetGuid", args => DoSomeActionWithStringToGetGuid((string)args[0]));
provider.Register("thenUseItForSomething", args => DoSomeActionWithAGuid((Guid)args[0],(bool)args[1]));
Guid guid = provider.Intercept<Guid>("doSomethingAndGetGuid", "I don't matter except if I am null");
bool isEmpty = guid == default(Guid);
provider.Intercept("thenUseItForSomething", guid, isEmpty);
}
private void DoSomeActionWithAGuid(Guid id, bool isEmpty)
{
// code
}
private Guid DoSomeActionWithStringToGetGuid(string arg1)
{
if(arg1 == null)
{
return default(Guid);
}
return Guid.NewGuid();
}
}
public class StringMethodProvider
{
private readonly Dictionary<string, Func<object[], object>> _dictionary = new Dictionary<string, Func<object[], object>>();
public void Register<T>(string command, Func<object[],T> function)
{
_dictionary.Add(command, args => function(args));
}
public void Register(string command, Action<object[]> function)
{
_dictionary.Add(command, args =>
{
function.Invoke(args);
return null;
} );
}
public T Intercept<T>(string command, params object[] args)
{
return (T)_dictionary[command].Invoke(args);
}
public void Intercept(string command, params object[] args)
{
_dictionary[command].Invoke(args);
}
}
The following scenario would allow you to use a dictionary of elements to send in as input parameters and get the same as the output parameters.
First add the following line at the top:
using TFunc = System.Func<System.Collections.Generic.IDictionary<string, object>, System.Collections.Generic.IDictionary<string, object>>;
Then inside your class, define the dictionary as follows:
private Dictionary<String, TFunc> actions = new Dictionary<String, TFunc>(){
{"getmultipledata", (input) =>
{
//DO WORKING HERE
return null;
}
},
{"runproc", (input) =>
{
//DO WORKING HERE
return null;
}
}
};
This would allow you to run these anonymous functions with a syntax similar to this:
var output = actions["runproc"](inputparam);
Why not use params object[] list for method parameters and do some validation inside either your methods (or calling logic), It will allow for a variable number of parameters.
Consider the following pseudo code:
TResult Foo<TResult>(Func<T1, T2,...,Tn, TResult> f, params object[] args)
{
TResult result = f(args);
return result;
}
The function accepts Func<> with unknown number of generic parameters and a list of the corresponding arguments. Is it possible to write it in C#? How to define and call Foo? How do I pass args to f?
You can use Delegate with DynamicInvoke.
With that, you don't need to handle with object[] in f.
TResult Foo<TResult>(Delegate f, params object[] args)
{
var result = f.DynamicInvoke(args);
return (TResult)Convert.ChangeType(result, typeof(TResult));
}
Usage:
Func<string, int, bool, bool> f = (name, age, active) =>
{
if (name == "Jon" && age == 40 && active)
{
return true;
}
return false;
};
Foo<bool>(f,"Jon", 40, true);
I created a fiddle showing some examples: https://dotnetfiddle.net/LdmOqo
Note:
If you want to use a method group, you need to use an explict casting to Func:
public static bool Method(string name, int age)
{
...
}
var method = (Func<string, int, bool>)Method;
Foo<bool>(method, "Jon", 40);
Fiddle: https://dotnetfiddle.net/3ZPLsY
That's not possible. At best, you could have a delegate that also takes a variable number of arguments, and then have the delegate parse the arguments
TResult Foo<TResult>(Func<object[], TResult> f, params object[] args)
{
TResult result = f(args);
return result;
}
Foo<int>(args =>
{
var name = args[0] as string;
var age = (int) args[1];
//...
return age;
}, arg1, arg2, arg3);
This could become easy with lambda expressions:
TResult Foo<TResult>(Func<TResult> f)
{
return f();
}
Then usage could be like:
var result = Foo<int>(() => method(arg1, arg2, arg3));
Where method can be arbitrary method returning int.
This way you can pass any number of any erguments directly through lambda.
To support asynchoronous code we can define:
Task<TResult> Foo<TResult>(Func<Task<TResult>> f)
{
return f();
}
// or with cancellation token
Task<TResult> Foo<TResult>(Func<CancellationToken, Task<TResult>> f, CancellationToken cancellationToken)
{
return f(cancellationToken);
}
and use it like:
var asyncResult = await Foo(async () => await asyncMethod(arg1, arg2, arg3));
// With cancellation token
var asyncResult = await Foo(
async (ct) => await asyncMethod(arg1, arg2, arg3, ct),
cancellationToken);
You could try something similar to what I posted here: https://stackoverflow.com/a/47556051/4681344
It will allow for any number of arguments, and enforces their types.
public delegate T ParamsAction<T>(params object[] args);
TResult Foo<TResult>(ParamsAction<TResult> f)
{
TResult result = f();
return result;
}
to call it, simply......
Foo(args => MethodToCallback("Bar", 123));
In some cases you may be able to get away with a trick like this:
public static class MyClass
{
private static T CommonWorkMethod<T>(Func<T> wishMultipleArgsFunc)
{
// ... do common preparation
T returnValue = wishMultipleArgsFunc();
// ... do common cleanup
return returnValue;
}
public static int DoCommonWorkNoParams() => CommonWorkMethod<int>(ProduceIntWithNoParams);
public static long DoCommonWorkWithLong(long p1) => CommonWorkMethod<long>(() => ProcessOneLong(p1));
public static string DoCommonWorkWith2Params(int p1, long p2) => CommonWorkMethod<string>(() => ConvertToCollatedString(p1, p2));
private static int ProduceIntWithNoParams() { return 5; }
}
Although it is not really what asked, a simple workaround would be to define several Foo method with different number of type arguments.
It is uncommon to have function with more than 6 parameters, so one could define the following method and get away with almost every use case, while staying type safe. Renan's solution could then be used for the remaining cases.
public TResult Foo<TResult> (Func<TResult> f)
{
return f();
}
public TResult Foo<T1, TResult>(Func<T1, TResult> f, T1 t1)
{
return f(t1);
}
public TResult Foo<T1, T2, TResult>(Func<T1, T2, TResult> f, T1 t1, T2 t2)
{
return f(t1, t2);
}
...
There is as far as I know no way to interact with reference types in Expression trees. (e.g. nothing emits a stind.* or a ldind.* opcode).
I'm working on a bit of a rewriter to get around this annoyance. Since I'm building a new type that has the method body replaced with delegate invocations (to get around the fact that CompileToMethod can only do static methods that can't interact with new members). For by-ref and out parameters, I thought I'd replace their usages with StrongBox<T>.
So if I came across a method that has a signature that looks like this::
public class SomeClass
{
public virtual bool SomeMethod(string arg1,ref int arg2)
{
}
}
The override, the callbase method, and the delegate field I generate will look like this::
public class SomeClass<1> : SomeClass
{
private static bool SomeMethod<0>(
SomeClass target,string arg1,StrongBox<int> arg2)
{
return call target.SomeMethod(arg1,ref arg2.Value)
}
private Func<SomeClass,string,StrongBox<int>,bool> <0>SomeMethod;
public override bool SomeMethod(string arg1,ref int arg2)
{
StrongBox<int> box = new StrongBox<int>();
box.Value = arg2;
bool retVal = <0>SomeMethod.Invoke(this,arg1,box);
arg2 = box.Value;
return retVal;
}
}
However, this is quite a lot of code to perform this conversion, for each parameter it introduces a lot of complexity. It would be much easier when I perform the setting of box.Value = arg2, if I could do something like &box.Value = &arg2 that is assign it's address to the address of arg2 as it stands. That way when the delegate performs a mutation on the value field the changes are forwarded. Doing this means I don't need to have to have a variable to hold the return value, and I don't need to perform a reference value update.
Alternatively, if there is a way to perform assign-by-ref semantics with Expression trees, I'm all ears of course.
Not sure if I really understand but maybe this is a solution:
class Program
{
public class SomeClass
{
private readonly int _n;
public SomeClass(int n) { _n = n; }
public virtual bool SomeMethod(string arg1, ref int arg2) {
if (String.IsNullOrWhiteSpace(arg1)) return false;
arg2 += arg1.Length + _n;
return true;
}
}
private delegate bool SomeDelegate(SomeClass that, string arg1, ref int arg2);
static void Main(string[] args) {
var instance = Expression.Parameter(typeof (SomeClass), "that");
var arg1Param = Expression.Parameter(typeof(string), "arg1");
var arg2Param = Expression.Parameter(typeof (int).MakeByRefType(), "arg2");
var someMethodInfo = typeof (SomeClass).GetMethod("SomeMethod");
var lambda = Expression.Lambda<SomeDelegate>(Expression.Call(instance, someMethodInfo, arg1Param, arg2Param), instance, arg1Param, arg2Param);
var someDelegate =lambda.Compile();
var myClass = new SomeClass(2);
var arg1 = "yup";
var arg2 = 1;
var result = someDelegate(myClass, arg1, ref arg2);
if(arg2 != 6) throw new Exception("Bad!");
Console.WriteLine("works...");
}
}
The important bit I think is typeof (int).MakeByRefType() .
How do I create a Dictionary where I can store functions?
Thanks.
I have about 30+ functions which can be executed from the user. I want to be able to execute the function this way:
private void functionName(arg1, arg2, arg3)
{
// code
}
dictionaryName.add("doSomething", functionName);
private void interceptCommand(string command)
{
foreach ( var cmd in dictionaryName )
{
if ( cmd.Key.Equals(command) )
{
cmd.Value.Invoke();
}
}
}
However, the function signature is not always the same, thus having different amount of arguments.
Like this:
Dictionary<int, Func<string, bool>>
This allows you to store functions that take a string parameter and return boolean.
dico[5] = foo => foo == "Bar";
Or if the function is not anonymous:
dico[5] = Foo;
where Foo is defined like this:
public bool Foo(string bar)
{
...
}
UPDATE:
After seeing your update it seems that you don't know in advance the signature of the function you would like to invoke. In .NET in order to invoke a function you need to pass all the arguments and if you don't know what the arguments are going to be the only way to achieve this is through reflection.
And here's another alternative:
class Program
{
static void Main()
{
// store
var dico = new Dictionary<int, Delegate>();
dico[1] = new Func<int, int, int>(Func1);
dico[2] = new Func<int, int, int, int>(Func2);
// and later invoke
var res = dico[1].DynamicInvoke(1, 2);
Console.WriteLine(res);
var res2 = dico[2].DynamicInvoke(1, 2, 3);
Console.WriteLine(res2);
}
public static int Func1(int arg1, int arg2)
{
return arg1 + arg2;
}
public static int Func2(int arg1, int arg2, int arg3)
{
return arg1 + arg2 + arg3;
}
}
With this approach you still need to know the number and type of parameters that need to be passed to each function at the corresponding index of the dictionary or you will get runtime error. And if your functions doesn't have return values use System.Action<> instead of System.Func<>.
However, the function signature is not
always the same, thus having different
amount of arguments.
Let's start with a few functions defined like this:
private object Function1() { return null; }
private object Function2(object arg1) { return null; }
private object Function3(object arg1, object arg3) { return null; }
You really have 2 viable options at your disposal:
1) Maintain type-safety by having clients call your function directly.
This is probably the best solution, unless you have very good reasons for breaking from this model.
When you talk about wanting to intercept function calls, it sounds to me like you're trying to re-invent virtual functions. There's a boat load of ways to get this sort of functionality out of the box, such as inheriting from a base class an overriding its functions.
It sounds to me like you want a class that's more of a wrapper than a derived instance of a base class, so do something like this:
public interface IMyObject
{
object Function1();
object Function2(object arg1);
object Function3(object arg1, object arg2);
}
class MyObject : IMyObject
{
public object Function1() { return null; }
public object Function2(object arg1) { return null; }
public object Function3(object arg1, object arg2) { return null; }
}
class MyObjectInterceptor : IMyObject
{
readonly IMyObject MyObject;
public MyObjectInterceptor()
: this(new MyObject())
{
}
public MyObjectInterceptor(IMyObject myObject)
{
MyObject = myObject;
}
public object Function1()
{
Console.WriteLine("Intercepted Function1");
return MyObject.Function1();
}
public object Function2(object arg1)
{
Console.WriteLine("Intercepted Function2");
return MyObject.Function2(arg1);
}
public object Function3(object arg1, object arg2)
{
Console.WriteLine("Intercepted Function3");
return MyObject.Function3(arg1, arg2);
}
}
2) OR map the input of your functions to a common interface.
This might work if all of your functions are related. For example, if you're writing a game, and all the functions do something to some part of the player or player's inventory. You'd end up with something like this:
class Interceptor
{
private object function1() { return null; }
private object function2(object arg1) { return null; }
private object function3(object arg1, object arg3) { return null; }
Dictionary<string, Func<State, object>> functions;
public Interceptor()
{
functions = new Dictionary<string, Func<State, object>>();
functions.Add("function1", state => function1());
functions.Add("function2", state => function2(state.arg1, state.arg2));
functions.Add("function3", state => function3(state.arg1, state.are2, state.arg3));
}
public object Invoke(string key, object state)
{
Func<object, object> func = functions[key];
return func(state);
}
}
Define the dictionary and add the function reference as the value, using System.Action as the type:
using System.Collections;
using System.Collections.Generic;
public class Actions {
public Dictionary<string, System.Action> myActions = new Dictionary<string, System.Action>();
public Actions() {
myActions ["myKey"] = TheFunction;
}
public void TheFunction() {
// your logic here
}
}
Then invoke it with:
Actions.myActions["myKey"]();
Hey, I hope this helps. What language are you coming from?
internal class ForExample
{
void DoItLikeThis()
{
var provider = new StringMethodProvider();
provider.Register("doSomethingAndGetGuid", args => DoSomeActionWithStringToGetGuid((string)args[0]));
provider.Register("thenUseItForSomething", args => DoSomeActionWithAGuid((Guid)args[0],(bool)args[1]));
Guid guid = provider.Intercept<Guid>("doSomethingAndGetGuid", "I don't matter except if I am null");
bool isEmpty = guid == default(Guid);
provider.Intercept("thenUseItForSomething", guid, isEmpty);
}
private void DoSomeActionWithAGuid(Guid id, bool isEmpty)
{
// code
}
private Guid DoSomeActionWithStringToGetGuid(string arg1)
{
if(arg1 == null)
{
return default(Guid);
}
return Guid.NewGuid();
}
}
public class StringMethodProvider
{
private readonly Dictionary<string, Func<object[], object>> _dictionary = new Dictionary<string, Func<object[], object>>();
public void Register<T>(string command, Func<object[],T> function)
{
_dictionary.Add(command, args => function(args));
}
public void Register(string command, Action<object[]> function)
{
_dictionary.Add(command, args =>
{
function.Invoke(args);
return null;
} );
}
public T Intercept<T>(string command, params object[] args)
{
return (T)_dictionary[command].Invoke(args);
}
public void Intercept(string command, params object[] args)
{
_dictionary[command].Invoke(args);
}
}
The following scenario would allow you to use a dictionary of elements to send in as input parameters and get the same as the output parameters.
First add the following line at the top:
using TFunc = System.Func<System.Collections.Generic.IDictionary<string, object>, System.Collections.Generic.IDictionary<string, object>>;
Then inside your class, define the dictionary as follows:
private Dictionary<String, TFunc> actions = new Dictionary<String, TFunc>(){
{"getmultipledata", (input) =>
{
//DO WORKING HERE
return null;
}
},
{"runproc", (input) =>
{
//DO WORKING HERE
return null;
}
}
};
This would allow you to run these anonymous functions with a syntax similar to this:
var output = actions["runproc"](inputparam);
Why not use params object[] list for method parameters and do some validation inside either your methods (or calling logic), It will allow for a variable number of parameters.
I am consuming a web service which has a number of methods (50) which create different objects.
example:
CreateObject1(Object1 obj, int arg2)
CreateObject2(Object2 obj, int arg2)
...
CreateObjectX(ObjectX obj, int arg2)
All Objects (Object1, Object2, ObjectX...) inherit from ObjectBase.
So I am trying to do this...
delegate void DlgtCreateObject(ObjectBase obj, int arg2);
public void CreateObject(ObjectBase obj, int arg2)
{
DlgtCreateObject dlgt;
string objType;
string operation;
objType = obj.GetType().ToString();
operation = "Create" + objType.Substring(objType.LastIndexOf(".") + 1);
using (MyWebService service = new MyWebService())
{
dlgt = (DlgtCreateObject)Delegate.CreateDelegate(typeof(DlgtCreateObject),
service,
operation,
false,
true);
dlgt(obj, arg2);
}
}
Unfortunately this gives me a Failed to Bind exception.
I believe this is because my delegate signature uses the ObjectBase as its first argument where the functions use the specific classes.
Is there a way around this?
If you're only trying to call the methods within here, I suggest you use Type.GetMethod and MethodBase.Invoke instead of going via delegates. Then you won't run into this problem.
Right after posting I figured generics might be the answer, and indeed the following seems to do the trick...
delegate void DlgtCreateObject<T>(T obj, int arg2) where T : ObjectBase;
public void CreateObject<T>(T obj, int arg2) where T : ObjectBase;
{
DlgtCreateObject dlgt;
string objType;
string operation;
objType = obj.GetType().ToString();
operation = "Create" + objType.Substring(objType.LastIndexOf(".") + 1);
using (MyWebService service = new MyWebService())
{
dlgt = (DlgtCreateObject<T>)Delegate.CreateDelegate(typeof(DlgtCreateObject<T>),
service,
operation,
false,
true);
dlgt(obj, arg2);
}
}