This question already has answers here:
Overloading assignment operator in C#
(3 answers)
Closed 2 years ago.
I have a complex object type for which I'm overriding the "base.ToString()" method so that it returns a string property value.
for example:
class foo
{
public string StringValue{get;set;}
public int SomeOtherValue{ get;set;}
public override ToString()
{
return StringValue;
}
}
So this allows me to use retrieve the value of the StringValue property easily.
Is there a way in which I can override or extend the base functionality so that I can use simple code such as below to set the StringValue property?
foo aFoo = new foo();
aFoo = "Some string value";
You can use implicit cast operator overload: http://msdn.microsoft.com/library/z5z9kes2.aspx
You can't overload the = operator as stated here
See this page for a complete list of overridable operators.
No, this is not possible. The assignment operator is not overridable and for good reason.
Developers are, even within the confines of C# and modern object-oriented programming languages, often "abusing" the system to make it do things it's not supposed to do. If you could assign a different meaning than passing a reference value to a variable to an assignment operator, think of the chaos that would create when inexperienced developers use it.
What you can do is to provide methods that allow your object to take its values from a string, like so:
afoo.TakeValuesFrom("Some string value");
or
MyThingy afoo = MyThingy.FromString("Some string value");
which would be almost identical to what you are asking, and perfectly legal and readable.
No you cannot. It is a protected part of the C# language specification. Being able to override this would be like overriding your bodies ability to breathe air with breathing water.
Use implicit conversion operators. It will do exactly what you need
Related
This question already has answers here:
Overloading assignment operator in C#
(3 answers)
Closed 2 years ago.
I have a complex object type for which I'm overriding the "base.ToString()" method so that it returns a string property value.
for example:
class foo
{
public string StringValue{get;set;}
public int SomeOtherValue{ get;set;}
public override ToString()
{
return StringValue;
}
}
So this allows me to use retrieve the value of the StringValue property easily.
Is there a way in which I can override or extend the base functionality so that I can use simple code such as below to set the StringValue property?
foo aFoo = new foo();
aFoo = "Some string value";
You can use implicit cast operator overload: http://msdn.microsoft.com/library/z5z9kes2.aspx
You can't overload the = operator as stated here
See this page for a complete list of overridable operators.
No, this is not possible. The assignment operator is not overridable and for good reason.
Developers are, even within the confines of C# and modern object-oriented programming languages, often "abusing" the system to make it do things it's not supposed to do. If you could assign a different meaning than passing a reference value to a variable to an assignment operator, think of the chaos that would create when inexperienced developers use it.
What you can do is to provide methods that allow your object to take its values from a string, like so:
afoo.TakeValuesFrom("Some string value");
or
MyThingy afoo = MyThingy.FromString("Some string value");
which would be almost identical to what you are asking, and perfectly legal and readable.
No you cannot. It is a protected part of the C# language specification. Being able to override this would be like overriding your bodies ability to breathe air with breathing water.
Use implicit conversion operators. It will do exactly what you need
It's possible to make a extension method for Object but not being able to use it on any derived class?
What a want is some general utilities to convert objects to certain types handling common exceptions. Ej. method for converting object to string but changing null to empty string and trimming white spaces.
object obj = ...
// I want to use de the method when the object is 'casted' as 'object':
string strValue = obj.ToStringTrim();
// But not be able to use it in any subclass. Ej. en this string:
strValue.ToStringTrim();
I know this is a tricky syntactic sugar and I supose the answer will be negative, and I should make a custom utility class for this kind of conversions, but just curious if it's possible...
EDIT
I know this is against inheritance, but I just wanted a hack, syntactic sugar or whatever... And already exists some in C# ;). And, why is this an issue? Well, it's not really an issue, but I don't want to have so much bloat on the autocomplete
No, that's not possible because that's not how inheritance works. A string is an Object. Period!
But why is that an issue? Don't use this extension with a string if you don't want.
However, the extension method could be implemented as:
public static string ToStringTrim(this Object obj)
{
return obj?.ToString().Trim() ?? "";
}
If obj is already a string then this is a no-op because String.ToString is implemented as return this.
This question already has answers here:
Solution for overloaded operator constraint in .NET generics
(4 answers)
What are generics in C#? [closed]
(3 answers)
Closed 6 years ago.
Generics are used to decouple logic from data type.
public class Calc<T>
{
public T Add(T a, T b)
{
return (a+b);
}
}
But this is throwing the below compile time error
Operator + cannot be applied on type T.
I am not understanding why so. because if it allows from main.cs
main()
{
Calc<int> obj = new Calc<int>();
int c = obj.Add(10,20);
}
Can somebody please explain why I am getting Build errors??
C# generics don't support arbitrary operators. The exact (possibly virtual) method must be known at compile-time of the generic type. Since the generic type argument in your example isn't constrained at all, you can only use the members of the object type, which doesn't include a + operator.
There's no way to use C# generics to do what you're trying to do, sorry. The best you can do is a bunch of type-checks for a few known types (and the appropriate casts, which are tricky with value types), or using reflection (dynamic in particular will work great).
Unrestricted generics like your Calc<T> must be able to compile with any type applied, not all types support the + operand so your code does not compile. This is regardless of what specific types you create your calling code with.
You can restrict the type of T and thus gain access to more methods by doing Calc<T> where T:object or Calc<T> where T: IComparable which would allow you to:
public T CompareTo(T a, T b)
{
return (a.CompareTo(b));
}
Since all T must now implement IComparable. Unfortunately Int32 does not implement any interface which defines the + operator or any addition method. So there is no way to implement that statement you are trying.
C# generics are different from C++ templates. The C# code cannot be compiled if generic type doesn't have definition for used method (operator+ in your case), while C++ compiler applies this method to the actual template argument type.
Addition is not allowed because there is no guarantee that passed types have operator + overload.
There is a way to accomplish that but it will work as long as you pass types that have operator +. Otherwise, RuntimeBinderException will be thrown. Also, there is some impact on performance, but unless code is performance critical, shouldn't be a problem.
public T Add<T>(T a, T b)
{
dynamic da = a, db = b;
return da + db;
}
This question already has answers here:
Implicit Conversion over a Collection
(4 answers)
Closed 7 years ago.
I created simple type that contains only one dependency property "Text" returns string. For easy conversion from string to my type I wrote this code:
public static implicit operator string(StringDP sdp)
{
return sdp.Text;
}
public static implicit operator StringDP(string str)
{
return new StringDP(str);
}
I want to have similar conversion from List<string> to List<myType>. Am I able to do this? Or I have to use something like this:
public List<string> Convert(List<myType> lst);
public List<myType> Convert(List<string> lst);
Thank you!
No, this is not possible. From the documentation:
Either the type of the argument to be converted, or the type of the result of the conversion, but not both, must be the containing type.
Both of the types involved in your hypothetical implicit conversion are concrete versions of the generic List<T> class. Since you can't add operators to the List<T> class yourself, and since that's where the implicit operators to achieve your goal would have to be, it can't be done.
Without more context, I admit that I can't really comment knowledgeably on the implicit conversion to and from string that you've defined. But in general, you should be very careful with implicit conversions. Assuming the implicit conversion of your type fits within the "safe" guidelines, then a conversion of a whole list of the type would be "fine".
This conversion can be done with custom methods such as your examples. Or you can use LINQ or the List<T>.ConvertAll() method. E.g.:
List<string> listOfString = listOfMyType.Select(item => (string)item).ToList();
List<myType> listOfMyType = listOfString.ConvertAll(item => (myType)item);
// etc.
However, even there I would suggest that you should be careful about how you are using something like that. It's one thing to convert a single instance of a value, but converting a whole collection involves quite a lot more overhead and most likely is not the correct way to solve the problem.
Not know what the actual problem is, I can't offer an alternative. Just to suggest you be very wary of the design path you appear to be headed down.
This might be a bit of an anti-pattern, but it is possible for a property on a C# class to accept multiple values?
For example, say I have an Public int property and I always want it to return an int, but I would like to be able to have the property set by assigning a decimal, an integer or some other data type. So my question is if it possible for properties to accept multiple values?
I think what you mean to ask is: How does implicit and explicit casting work for int and decimal?
You are asking about implicit casting which automatically coverts one object to another defined type. You will not be able to do this for an int and decimal because they are already defined in the framework and you are not able to reduce the scope of the decimal by casting it to an int. But if you were using that as an example for actual objects that you created you can use the implicit link above, to learn more about how this works and how to implement it.
But you can always use the convert method to convert them to the right type;
public int MyProperty { get; set; }
...
obj.MyProperty = Convert.ToInt32(32.0M);
obj.MyProperty = Convert.ToInt32(40.222D);
obj.MyProperty = Convert.ToInt32("42");
Edit: This method can't be used since the op is specifically bound to properties.
I do not believe this is possible with the robustness that you describe. In this case you would likely be better off using an overloaded method (polymorphism).
This is what is typically known as a setter (or mutator) and you can overload the method to accept multiple different types of parameters. Each will perform differently if you wish. The way I have them set up might not be syntactically correct but that is the general idea you're looking for I believe.
public class MyClass {
private Int32 mySomeValue;
public void setSomeValue(Double value) { this.mySomeValue = Convert.ToInt32(value); }
public void setSomeValue(Int32 value) { this.mySomeValue = value; }
}
No. A property has a single value. You can assign anything to it that could be assigned to a variable of the same type.
It seems like you would have to ascertain the type at run-time. You could have the property accept an object, determine the type and take your action. You would have to throw exceptions for things you don't expect, of course. Like you say, probably not the best, but possible. :)
Properties are supposed to look sort of like public fields. Create setter-methods, or do the cast/conversion in the assignment statements as opposed to in the property-setter.