I notice that an implicit operator is required to be called static but it actually is not really static at all... How come the implicit operator cannot be accessed statically but it can be accessed through an instance. This is the complete opposite of static. Suppose I wanted a static static implicit operator so that I could implicitly convert the static states of a class.
For example
a = new b(); // implicitly converts b to a.
a = b(); // implicitly convert the static states of b to a.
So for example b is a non-static class because it has a form but for all intents and purposes it is static and all instances are sharing the same information so I want to implicitly convert the class' static internals.
I will try to go into more detail of my example since Jeff thinks it makes no sense.
class b displays a dialog form, but it saves all the information entered into static variables. This is because the instances of b are only to display the dialog form and the data entered is one logical block of data(there is only one logical instance of the data entered). All the static variables fit directly into class a and so I can seamlessly convert the static variables in b to an instance of a class, however I would like to use implicit operator for this task instead of having a separate method. But it laments me that I cannot have an actual static implicit operator. Perhaps I am misunderstanding the word static and I am only using it in terms of how it works with methods and classes.
If an operator was not static, it could not handle null operands.
This applies equally to the case of an implicit conversion operator:
public class MyClass
{
public MyClass(int x)
{
this.X = x;
}
public int X { get; private set; }
public static implicit operator int(MyClass operand)
{
if (operand == null)
{
return 0;
}
return operand.X;
}
}
internal class Program
{
internal static void Main(string[] args)
{
MyClass x = null;
int y = x; // What instance would a non-static operator use here?
}
}
In C#, all operator definitions are static, see for instance http://msdn.microsoft.com/en-us/library/aa288467(v=vs.71).aspx
-Binary operator definitions, of course, because it would be arbitrary to declare one or the other to be this.
-Unary operator definitions, to match the theme of binary operator definitions being static.
It is just convention that it is done this way.
No operator works on the 'static state' of a class (except possibly typeof). In other words it's not possible to do anything like this:
var result = System.Int32 + System.Int32;
Operators only work on instances of a class.
int a = ..., b = ...;
var result = a + b;
All operators are necessarily static, so there's no need to disambiguate between 'normal static' operators and 'static static' operators.
You might consider using a singleton pattern. Something like this:
public class Foo
{
public int Member { get; set; }
private static Foo instance = new Foo();
public static Foo Instance { get { return instance; } }
private Foo()
{
}
public static implicit operator int(Foo foo)
{
return foo.Member;
}
}
Then you can use it as:
int a = Foo.Instance;
Here's a second answer from me, trying to guess at your underlying problem (instead of answering the question in the title, as I did in my first answer):
From the editted question and comments, it looks like you are trying to:
ensure that there is only a single instance of an InputBox class.
Convert data in the input box class to a string.
I'd make sure that you really need to enforce only a single instance of the InputBox class, but if that requirement is well founded then you could do something like this, using the Singleton pattern, and overriding the ToString instance method.:
class InputBox
{
static InputBox Instance = new InputBox();
int someNumber;
string someText;
private InputBox()
{
}
// ...
public override string ToString()
{
return someNumber.ToString() + " " + someText;
}
}
Usage:
string result = InputBox.Instance.ToString();
Addendum:
If it's really all about the syntax you want to use, you could add a delegate like this:
// Please don't really do this ;)
Func<string> InputBox = () => MyNamespace.InputBox.Instance.ToString();
And then use it like this:
string result = InputBox();
But anyone reading your code would cry ;)
Related
Basically I want to use my own types instead of primitives like int/double, but still pass around these primitive values. Something like:
interface IInt {} // My interface to represent int. If I could fake so "int" implements this, all would work.
interface IPostNumber : IInt {} // Post number is an int. But int is not type safe enough for me.
void MyFunction(IPostNumber postNumber); // My function that should accept int/IPostNumber.
MyFunction(42); // This could also work with implicit conversion, but not allowed for interfaces:(
From ispiro's suggestion I found something that should cover everything.
So I declare my interfaces independent of underlying representation, e.g.
public interface IPostNumber{}
public interface IPostNumberFrom : IPostNumber{}
public interface IPostNumberTo : IPostNumber{}
These have full interface generality such as multiple inheritance. Then the data representation is done with generic classes with implicit conversion:
public class CInt<T>
{
public int value;
public static implicit operator int(CInt<T> d) => d.value;
public static implicit operator CInt<T>(int b) => new CInt<T>() { value = b };
}
Functions that accepts IPostNumber with int, is done as such:
private int TestPostNumberInt(CInt<IPostNumber> i) => i;
private int TestPostNumberFrom(CInt<IPostNumberFrom> i) => i;
CInt<IPostNumber> a = 4; // Works
Assert.Equal(1, TestPostNumberInt(1)); // Works
Assert.Equal(1, TestPostNumberFrom(a)); // Don't compile with IPostNumber into IPostNumberFrom
Now I can always declare CString<IPostNumber>, if some post numbers are represented with string. Or a function could accept the IPostNumber interface itself, if I make some class of it. Now one little issue is that if I want to pass CInt<IPostNumberFrom> to TestPostNumber, the method must be generic with T : IPostNumber, like this:
private int TestPostNumberInt<T>(CInt<T> i) where T : IPostNumber => i;
private int TestPostNumberIntFrom<T>(CInt<T> i) where T : IPostNumberFrom => i;
and then the generic type will not be detected while using implicit conversion (must cast). But we'll see if this is a big deal.
Also for later consideration: I will have class CJSON<T> : CString<T>. From what I see it works, though argubly CJSON could have different representations as well, like byte[] in some context. (But this is taking things far). So just need to think hard about representation vs. interfaces for my domain concepts.
I think what you might be looking for are implicit operators, but unfortunately I believe they're not supported for interfaces in the C# language specification. You can do this with subclasses if need be. Here's an example:
public class MyInt
{
int SomeValue;
public TestInt(int i)
{
SomeValue = i;
}
public static implicit operator MyInt(int i)
{
return new MyInt(i);
}
public static implicit operator int(MyInt myInt)
{
return myInt.SomeValue;
}
}
To assign using an implicit operator, you can do this:
MyInt n = 3;
int x = n;
See: implicit operator using interfaces
Is it this you're looking for?
public class IInt
{
public int TheInt;
public IInt(int theInt)
{
TheInt = theInt;
}
}
and then either use:
IInt i = new IInt(42);
MyFunction(i);
or define MyFunction for int and then use:
IInt i = new IInt(42);
MyFunction(i.TheInt);
Just one more idea:
public class IInt<T> where T : struct
{
public T TheInt;
public IInt(T theInt)
{
TheInt = theInt;
}
}
You can create an extension method but that method should be explicitly called.
My class looks something like this:
public class Testclass
{
public int myValue;
}
In another context I want to simply check the value of myValue against 0.
So I would write:
Testclass tc = new Testclass();
tc.myValue = 13;
if (tc.myValue == 0)
{
}
How would it be possible to simplify this so that the Testclass object knows when it is compared to a boolean? (or used as a boolean value) to write:
Testclass tc = new Testclass();
tc.myValue = 13;
if (tc)
{
}
To be more precise, the Testclass will be the result of another method that is included in a library, so the code would look like this:
anotherClass ac =new anotherClass();
// if (ac.AMethod().myValue == 0)
// should be
if (ac.AMethod())
{
}
Where AMethod would look like this:
public Testclass AMethod()
{
return new Testclass();
}
[Edit at 2016-04-13]:
Like Dennis wrote, i am using
public static implicit operator bool(TestClass value)
to get the "Boolean Value" of my class. To be a bit more precise and to stick more to my real application i would like to change the signature to
public static implicit operator UInt64(FlexComDotNetFehler fehler)
public static implicit operator Boolean(FlexComDotNetFehler fehler)
So these two methods of class FlexComDotNetFehler return the internal UInt64 field in the first case as the real representation as UInt64and in the second one as a Boolean value, that is true, when the UInt64 value is > 0.
But now, when i code
FlexComDotNetFehler x;
FlexComDotNetFehler y;
if (x == y)
where x and y are both of type FlexComDotNetFehler
the compiler cant know if it should use the Boolean or the UInt64 operator.
So i wrote
if ((UInt64)x != (UInt64)y)
but then those two type casts are greyed out.
#Ɖiamond ǤeezeƦ: thanks for your reformatting and editing. But I think now i got i right?
Greetings Wolfgang
BTW is there a playground where i can test the formatting and its output? And how do i send private messages to other users?
Define implicit cast operator for TestClass:
class TestClass
{
public int myValue;
public static implicit operator bool(TestClass value)
{
// assuming, that 1 is true;
// somehow this method should deal with value == null case
return value != null && value.myValue == 1;
}
}
Also think about converting TestClass from class to structure (see this reference). If you'll decide to convert it, avoid mutable structures.
you can use extension methods to implement method you can use any time not only for this class Testclass
public static class IntExtension
{
public static bool IsBool(this int number)
{
bool result = true;
if (number == 0)
{
result = false;
}
return result;
}
}
and then yo can
if ((ac.AMethod()).IsBool())
{}
public class SampleClass {
public int value;
public SampleClass(int v)
{ value = v; }
}
// i want to access value like this
SampleClass sc = new SampleClass(5);
int i = sc;
Is there a way to do this in C#? I don't want to have to say sc.Value every time i need to access the value.
Use an implicit conversion:
public class SampleClass {
public int value;
public SampleClass(int v)
{ value = v; }
public static implicit operator int (SampleClass c)
{
return c.value;
}
}
You should look into properties however.
You can do it by including an implicit conversion from SampleClass to int:
public static implicit operator int(SampleClass s)
{
return s.value;
}
... but I would strongly recommend that you don't do so, or at least that you think very carefully beforehand. Implicit conversions make it harder to reason about the language in various ways (consider things like overload resolution, for example).
Very, very occasionally it's a good idea to introduce implicit conversions - for example LINQ to XML makes great use of it with string to XNamespace and string to XName conversions - but I wouldn't do it here just to avoid having to use .Value.
It's slightly more reasonable to make an explicit conversion (just change implicit to explicit in the operator conversion) in that at least that makes it clear-ish what's going on in the calling code... but at that point there's really not much difference in source size between a cast to int and using .Value.
(And as suggested elsewhere, don't make fields public - use properties instead.)
Take a look at this. You need to overload the implicit cast operator for int.
Yes, it's possible. You need to implement implicit for your SampleClass:
Here it is:
public class SampleClass
{
public int Value;
public SampleClass(int v)
{
Value = v;
}
public static implicit operator int(SampleClass d)
{
return d.Value;
}
}
I tried to do something like this:
m_mystruct = (Form1.mystruct)m_myclass.mystruct;
where both structs have same definition.
C# doesn't want to do the cast.
Update: instead of why, I modify my question
How do I pass a struct from a class to a winform ?
Having the "same definition" doesn't make them the same type.
In fact, if there are two definitions, then they are two different types.
Because, while the have the same definition, they are not related in any way.
If you want to be able to cast between the two types, you have to define the explicit/implicit conversions.
If they are defined in two separate places then they are actually two different types.
You could define explicit and implicit operators to convert between the two. It might look like this.
public struct Foo
{
public int Value;
public static explicit operator Bar(Foo source)
{
var destination = new Bar();
destination.Value = source.Value;
return destination;
}
}
public struct Bar
{
public int Value;
public static explicit operator Foo(Bar source)
{
var destination = new Foo();
destination.Value = source.Value;
return destination;
}
}
Think about whether you really need two different declarations. But, whatever you decide do not do the following unless you absolutely have no other choice. It could go wrong in so many different ways.
Foo f = new Foo();
IntPtr pf = Marshal.AllocHGlobal(Marshal.SizeOf(f));
Marshal.StructureToPtr(f, pf, false);
Bar b = (Bar)Marshal.PtrToStructure(pf, typeof(Bar));
Marshal.FreeHGlobal(pf);
or
unsafe
{
Foo f = new Foo();
Bar b = *(Bar*)&f;
}
They are basically different types!
How would you do specialization in C#?
I'll pose a problem. You have a template type, you have no idea what it is. But you do know if it's derived from XYZ you want to call .alternativeFunc(). A great way is to call a specialized function or class and have normalCall return .normalFunc() while have the other specialization on any derived type of XYZ to call .alternativeFunc(). How would this be done in C#?
In C#, the closest to specialization is to use a more-specific overload; however, this is brittle, and doesn't cover every possible usage. For example:
void Foo<T>(T value) {Console.WriteLine("General method");}
void Foo(Bar value) {Console.WriteLine("Specialized method");}
Here, if the compiler knows the types at compile, it will pick the most specific:
Bar bar = new Bar();
Foo(bar); // uses the specialized method
However....
void Test<TSomething>(TSomething value) {
Foo(value);
}
will use Foo<T> even for TSomething=Bar, as this is burned in at compile-time.
One other approach is to use type-testing within a generic method - however, this is usually a poor idea, and isn't recommended.
Basically, C# just doesn't want you to work with specializations, except for polymorphism:
class SomeBase { public virtual void Foo() {...}}
class Bar : SomeBase { public override void Foo() {...}}
Here Bar.Foo will always resolve to the correct override.
Assuming you're talking about template specialization as it can be done with C++ templates - a feature like this isn't really available in C#. This is because C# generics aren't processed during the compilation and are more a feature of the runtime.
However, you can achieve similar effect using C# 3.0 extension methods. Here is an example that shows how to add extension method only for MyClass<int> type, which is just like template specialization. Note however, that you can't use this to hide default implementation of the method, because C# compiler always prefers standard methods to extension methods:
class MyClass<T> {
public int Foo { get { return 10; } }
}
static class MyClassSpecialization {
public static int Bar(this MyClass<int> cls) {
return cls.Foo + 20;
}
}
Now you can write this:
var cls = new MyClass<int>();
cls.Bar();
If you want to have a default case for the method that would be used when no specialization is provided, than I believe writing one generic Bar extension method should do the trick:
public static int Bar<T>(this MyClass<T> cls) {
return cls.Foo + 42;
}
I was searching for a pattern to simulate template specialization, too. There are some approaches which may work in some circumstances. However what about the case
static void Add<T>(T value1, T value2)
{
//add the 2 numeric values
}
It would be possible to choose the action using statements e.g. if (typeof(T) == typeof(int)). But there is a better way to simulate real template specialization with the overhead of a single virtual function call:
public interface IMath<T>
{
T Add(T value1, T value2);
}
public class Math<T> : IMath<T>
{
public static readonly IMath<T> P = Math.P as IMath<T> ?? new Math<T>();
//default implementation
T IMath<T>.Add(T value1, T value2)
{
throw new NotSupportedException();
}
}
class Math : IMath<int>, IMath<double>
{
public static Math P = new Math();
//specialized for int
int IMath<int>.Add(int value1, int value2)
{
return value1 + value2;
}
//specialized for double
double IMath<double>.Add(double value1, double value2)
{
return value1 + value2;
}
}
Now we can write, without having to know the type in advance:
static T Add<T>(T value1, T value2)
{
return Math<T>.P.Add(value1, value2);
}
private static void Main(string[] args)
{
var result1 = Add(1, 2);
var result2 = Add(1.5, 2.5);
return;
}
If the specialization should not only be called for the implemented types, but also derived types, one could use an In parameter for the interface. However, in this case the return types of the methods cannot be of the generic type T any more.
By adding an intermediate class and a dictionary, specialization is possible.
To specialize on T, we create an generic interface, having a method called (e.g.) Apply. For the specific classes that interface is implemented, defining the method Apply specific for that class. This intermediate class is called the traits class.
That traits class can be specified as a parameter in the call of the generic method, which then (of course) always takes the right implementation.
Instead of specifying it manually, the traits class can also be stored in a global IDictionary<System.Type, object>. It can then be looked up and voila, you have real specialization there.
If convenient you can expose it in an extension method.
class MyClass<T>
{
public string Foo() { return "MyClass"; }
}
interface BaseTraits<T>
{
string Apply(T cls);
}
class IntTraits : BaseTraits<MyClass<int>>
{
public string Apply(MyClass<int> cls)
{
return cls.Foo() + " i";
}
}
class DoubleTraits : BaseTraits<MyClass<double>>
{
public string Apply(MyClass<double> cls)
{
return cls.Foo() + " d";
}
}
// Somewhere in a (static) class:
public static IDictionary<Type, object> register;
register = new Dictionary<Type, object>();
register[typeof(MyClass<int>)] = new IntTraits();
register[typeof(MyClass<double>)] = new DoubleTraits();
public static string Bar<T>(this T obj)
{
BaseTraits<T> traits = register[typeof(T)] as BaseTraits<T>;
return traits.Apply(obj);
}
var cls1 = new MyClass<int>();
var cls2 = new MyClass<double>();
string id = cls1.Bar();
string dd = cls2.Bar();
See this link to my recent blog and the follow ups for an extensive description and samples.
I think there is a way to achieve it with .NET 4+ using dynamic resolution:
static class Converter<T>
{
public static string Convert(T data)
{
return Convert((dynamic)data);
}
private static string Convert(Int16 data) => $"Int16 {data}";
private static string Convert(UInt16 data) => $"UInt16 {data}";
private static string Convert(Int32 data) => $"Int32 {data}";
private static string Convert(UInt32 data) => $"UInt32 {data}";
}
class Program
{
static void Main(string[] args)
{
Console.WriteLine(Converter<Int16>.Convert(-1));
Console.WriteLine(Converter<UInt16>.Convert(1));
Console.WriteLine(Converter<Int32>.Convert(-1));
Console.WriteLine(Converter<UInt32>.Convert(1));
}
}
Output:
Int16 -1
UInt16 1
Int32 -1
UInt32 1
Which shows that a different implementation is called for different types.
Some of the proposed answers are using runtime type info: inherently slower than compile-time bound method calls.
Compiler does not enforce specialization as well as it does in C++.
I would recommend looking at PostSharp for a way to inject code after the usual compiler is done to achieve an effect similar to C++.
A simpler, shorter and more readable version of what #LionAM proposed (about half of the code size), shown for lerp since this was my actual use case:
public interface ILerp<T> {
T Lerp( T a, T b, float t );
}
public class Lerp : ILerp<float>, ILerp<double> {
private static readonly Lerp instance = new();
public static T Lerp<T>( T a, T b, float t )
=> ( instance as ILerp<T> ?? throw new NotSupportedException() ).Lerp( a, b, t );
float ILerp<float>.Lerp( float a, float b, float t ) => Mathf.Lerp( a, b, t );
double ILerp<double>.Lerp( double a, double b, float t ) => Mathd.Lerp( a, b, t );
}
You can then just e.g.
Lerp.Lerp(a, b, t);
in any generic context, or provide the method as a grouped Lerp.lerp method reference matching T(T,T,float) signature.
If ClassCastException is good enough for you, you can of course just use
=> ( (ILerp<T>) instance ).Lerp( a, b, t );
to make the code even shorter/simpler.
If you just want to test if a type is derrived from XYZ, then you can use:
theunknownobject.GetType().IsAssignableFrom(typeof(XYZ));
If so, you can cast "theunknownobject" to XYZ and invoke alternativeFunc() like this:
XYZ xyzObject = (XYZ)theunknownobject;
xyzObject.alternativeFunc();
Hope this helps.