Is there a way to "tell" a method with optional parameters to use the default values, beyond omitting the parameter? I imagine the syntax would look something like this:
DoSomething(myParam: default) //calling the method
public void DoSomething(int myParam = 5) { ... } //method definition
The reason for doing this is to avoid ambiguity between an overload of this method that takes no parameters. In other words, I don't want this method to be called:
public void DoSomething() { ... }
Thanks in advance.
If you don't want the user to call the DoSomething method that takes no parameters, just make it private like so:
private void DoSomething();
It seems like in this particular case you just shouldn't be using optional parameters at all. They are designed to make your life easy. When they stop doing that it's probably time to just stop using them.
You can accomplish the same general goal of optional parameters with various overloads using this general approach:
public void Foo(int param1, int param2, int param3){ /* actual Foo code goes here */ }
public void Foo(int param1, int param2) { Foo(param1, param2, 5); }
public void Foo(int param1) { Foo(param1, 0, 5); }
public void Foo() { Foo(42, 0, 5); }
This is what optional parameters were designed to avoid, but sometimes going back to this boilerplate code can be simpler, even if it bloats the code a tad.
Related
I have a private method I would like to allow access to only to be passed as a delegate but not be executed otherwise.
for example:
class a
{
public delegate int myDelegate(int a);
public static int myMethod(int data, myDelegate action)
{
//my code
}
private static int methodA(int a){ //code}
private static int methodb(int a){ //code}
}
class b
{
public void anotherMethod()
{
var doAction = new myDelegate(methodA);
result = myMethod(8, doAction);
}
}
so in my example I would like methodA and MethodB to only be executed from within class a, but still enabling access to them so they can be used as delegates to be passed to methods from class a.
is it at all possible?
currently I am getting an error "methodA is inaccessible due to protection level"
What you are saying is not possible. Once a class has an instance of a delegate, no one can stop it from calling it. So if class B were able to pass a delegate to myMethod, it would also be able to call that delegate directly, unless methodA and methodB need special parameters, that only A knows about, to do anything useful.
One way of doing something similar is to create an enum called something like MethodOfA and declare MethodA and MethodB as the possible values of the enum. In class A declare a private Dictionary<MethodOfA, MyDelegate> methodDict that records what each enum value correspond to. Then declare another overload of myMethod that takes a MethodOfA like this:
public static int myMethod(int data, MethodOfA action)
=> myMethod(data, methodDict[action]);
Nevertheless, this looks like bad design to me. Maybe you don't need the overload of myMethod(int, MyDelegate) in the first place, and just check the enum to perform the corresponding action. The other thing that you might try is the strategy pattern.
If I'm understanding you correctly, you'd like to know how to use delegates (pass actions / functions) as parameters?
If so, then you should use Action<> and/or Func<> as they're delegates. Your code could look like this then:
class a
{
public int myMethod(int data, Func<int, int> func)
{
return func.Invoke(data);
}
}
class b
{
public void anotherMethod()
{
var classA = new a();
var result = classA.myMethod(8, Double);
}
private int Double(int i)
{
return i * 2;
}
}
Is there a way I can pass through an argument to an Action without using an anonymous function?
Eg, the following code works fine:
private void doSomethingAndLogIt(string log, Action dosomething)
{
Debug.WriteLine(log);
dosomething();
}
private void multiplyIt()
{
_result = "great";
}
...
doSomethingAndLogIt("Did something", multiplyIt);
but what I want to do is this:
private void doSomethingAndLogIt(string log, Action<int> dosomething)
{
Debug.WriteLine(log);
dosomething(???);
}
private void multiplyIt(int a)
{
_result = "great";
}
doSomethingAndLogIt("Did something", multiplyIt(5));
I realise that I can do this:
private void doSomethingAndLogIt(string log, Action<int> dosomething, int inputValue)
{
Debug.WriteLine(log);
dosomething(inputValue);
}
private void multiplyIt(int a)
{
_result = "great";
}
doSomethingAndLogIt("Did something", multiplyIt, 5);
but it's pretty confusing. I also realise that I can do this:
doSomethingAndLogIt("Did something", () => {
multiplyIt(5);
});
but it would be great if I could do this:
doSomethingAndLogIt("Did something", multiplyIt(5));
You do not need to do anything special. This code below:
doSomethingAndLogIt("Test", () => multiplyIt(5));
will already do what you are after. When the delegate is called, the parameter 5 will be passed in as well. Why? Because the callee will call your delegate, and you will call the method multiply with the argument 5.
Here is a quick test.
It isn't possible to do that as of the current version of C#, here's why...
Let's take your example (fake syntax)
public int MultiplyIt(int value)
{
//Do something that has side-effects
}
public void SomeMethod(Action<int> someAction<int>)
{
//Do something
someAction();
}
Now let's create an override of that method:
public void SomeMethod(int someValue)
{
//Do something
}
Now you call it:
SomeMethod(multiplyIt(5))
Which one does the compiler call?
Lets say you don't overload it (or that for some reason the compiler shouts an error if you do, but it is legal).
What then is the difference between these two calls?
SomeMethod(multiplyIt(5));
SomeMethod(() => multiplyIt(5));
Technically the first one runs multiplyIt before passing its value to SomeMethod. The second one multiplyIt may never be called, or it may alter something and then call it. That is an important distinction. If you add in some method to call it without the () => part, the developer can't know, without reading documentation, how the method call (and the action) are called. Is it a normal method call? The "special" delegate case? Who knows.
The () => isn't that much of a price to pay to be able to read a method and understand that you are passing in a delegate vs a value.
using System;
using System.Collections.Generic;
namespace Generics
{
class Minivan
{
public void foo(int z, int x)
{
Console.WriteLine("foo with two parameters");
}
public void foo(params int[] z)
{
Console.WriteLine("foo with two params parameter");
}
}
class D
{
public static void Main()
{
Minivan car3 = new Minivan();
car3.foo(10,20); // which method will be called here!!!
}
}
}
which foo method is called? and why?
in a simple sentence "more specific is better than less specific"
so public void foo(int z, int x) will be called.
it is because of method overload resolution rules in C#.
you can read more in this answer
Compiler will choose a method with explicit parameters (as said in c# spec). But if you'll call method with 3 params the params implementation'll be called
To put it simply, the one with the two explicit parameters is chosen here.
I don't claim to know the reasoning behind that decision in the spec, but I would image it goes something like "You went to the trouble to explicitly handle the case where two parameters are passed in, so that would be the only sensible choice of method to choose"
this is a simple overload, when you explicitly call the function with two parameters it will call public void foo(int z, int x)
I'm in a case where I would like to have a method that can take other methods as input.
The input method will always have a single object as input, but the objects are different.
This is more or less what i need to be able to do:
public static void takeAnything(Action<object> inputFunc)
{
Console.WriteLine(inputFunc.Method.Name);
}
public static void test1(MyOwnObject input){
// Do stuff with input object
}
public static void test2(MyOtherOwnObject input){
// Do stuff with input object
}
public static void startSystem(){
takeAnything(test1);
takeAnything(test2);
}
Which in this dummy case would write out:
test1
test2
I just cant't get this to work, so any help would be very much appreciated.
EDIT
I do not know if this is possible, maybe it is not, but it is important that the call is just takeAnything(test1), not takeAnything<MyOwnObject>(test1) or anything else.
Make your method generic
public static void TakeAnything<T>(Action<T> inputFunc)
{
Console.WriteLine(inputFunc.Method.Name);
}
Of course, you will be able only to pass methods which have single input argument.
UPDATE: Unfortunately C# cannot infer action generic parameter type from usage, when you are passing method group to method, so only way to use it is specifying generic parameter type manually
takeAnything<MyOwnObject>(test)
For details see question C# 3.0 generic type inference - passing a delegate as a function parameter
Try this, so you can pass dynamic parameters to action:
public static void takeAnything(Expression<Action> inputFunc)
{
var currentMethod = ((MethodCallExpression)inputFunc.Body);
Console.WriteLine(currentMethod.Method.Name);
}
public static void test(MyOwnObject input){
// Do stuff with input object
}
public static void startSystem(){
MyOwnObject yourObject = new MyOwnObject();
takeAnything(() => test(yourObject));
}
Why not change the header of your takeAnything method to:
public static void takeAnything(Action<MyOwnObject> inputFunc)
I have a method that I call multiple times, but each time a different method with a different signature is called from inside.
public void MethodOne()
{
//some stuff
*MethodCall();
//some stuff
}
So MethodOne is called multiple times, each time with a different *MethodCall(). What I'm trying to do is something like this :
public void MethodOne(Func<> MethodCall)
{
//some stuff
*MethodCall;
//some stuff
}
but the Methods that are called each have a different return type and different parameters. Is there a way to do this using Functors? If not, how would I go about doing this?
Thank you!
You best bet would be to use the non-generic Action type (or MethodInvoker would be the same), i.e.
public void MethodOne(Action callback)
{
//some stuff
if(callback != null) callback();
//some stuff
}
From this you can call any method by wrapping it at the caller, i.e.
MethodOne(SimpleMethod); // SimpleMethod has no parameters and returns void
MethodOne(() => MoreComplexMethod(1, "abc")); // this one returns void
MethodOne(() => { MethodThatReturnsSomething(12); }); // anything you like
etc
You cannot call a function which requires parameters without supplying them, so the answer is "no, not possible"
Also, maybe you want the following:
void MethodOne(Action a)
{
// some stuff
a();
// some stuff
}
... // somewhere in the code
MethodOne((Action)(() => { DoSomethingOther(1, 2, 3); }));
MethodOne((Action)(() => { DoSomethingEvenDifferent(1, 2, 3, 4, 5); }));
Every delegate in .Net is an instance of a class derived from Delegate. So if you really wish to pass 'any' delegate to a method, you can pass it as Delegate
To invoke it, you need to use its DynamicInvoke method.
public void MethodOne(Delegate MethodCall)
{
//some stuff
//Assuming you now have the required parameters
//or add params object[] args to the signature of this method
object res = MethodCall.DynamicInvoke(args); //args is object[] representing the parameters
//some stuff
}
But this is not recommended as DynamicInvoke is slow and it does not offer any compile time safety. Probably you should revisit your design.
This is basically not possible. You could make MethodOne generic for the return type, and use a lambda that closes over its outside block instead of parameters:
static void Main(string[] args)
{
int parameterSubst = 1;
int result = MethodOne<int>(() => parameterSubst);
string result2 = MethodOne<string>(() =>
{
string s = parameterSubst.ToString();
s += "foo";
return s;
});
}
static T MethodOne<T>(Func<T> function)
{
return function();
}
As you can see, parameterSubst is used in the passed Func<T>s, but not as a parameter.