I need to overload some operators when called using Double types. To achieve this, I'm creating a class MyDouble, which inherits from Double. MyDouble looks somewhat like this
class MyDouble : Double
{
Double value;
// operator overloads go here
}
I want to abstract away the value property from the user so that it is usable just as a Double. Basically I want the user to be able to do this:
MyDouble a = 5; //a.value gets assigned 5
Console.WriteLine(a); //prints a.value
I don't want the user to have to specifically target the value property. Is this possible? How would I go about it?
You can define an implicit conversion operator, like this:
class MyDouble {
public Value {get; private set;}
public Double(double value) {
Value = value;
}
// Other declarations go here...
public static implicit operator double(MyDouble md) {
return md.Value;
}
public static implicit operator MyDouble(double d) {
return new MyDouble(d);
}
}
Related
I'm very fresh to C#
Currently learning Operator overloading
i'm trying to do something like this:
string val = 500; (I can't implicitly)
and then
Number n1 = val;
I manages to get the Number n1 = someintvalue, for instance:
Number n1 = 500;
like this:
public struct Number
{
public int Value { get; set; }
public Number(int Val)
{
Value = Val;
}
public static implicit operator Number(int num)
{
return new Number(num);
}
}
However, when trying to make Number n1 = val; (when val is a string)
I simply cant since the first line cant compile:
string val = 500;
and the following wont work:
public static implicit operator string(int A)
{
return new string(A);
}
because of 1 error which i can not understand
1)User-defined conversion must convert to or from the enclosing type
by the way i get the idea of op overload
underthis specific case of: return new Number(num);
I simply init the ctor
still need some more fundemental understanding
thx ahead!
I presume the function you quote is within the Number class. You have added a conversion operator from an int to a string within that class, which is not legal. You can only add operators that convert to or from the type they're defined in, such as:
public static implicit operator string(Number A)
{
return new string(A.Value);
}
which will fail because string does not have a constructor that takes an int. You could do:
public static implicit operator string(Number A)
{
return A.ToString();
}
But the standard way to "convert" to a string is to overload the ToString method, which the compiler often calls automatically when a conversion to string is requested:
public override string ToString()
{
return Value.ToString();
}
Is there a way I can overload primitives, for example addition with doubles? I want to automatically round the doubles whenever an operation is performed. My current code is this:
class Test{
public static double operator +(double x, double y){
return Math.Round(x + y)
}
}
but there's an unfortunate error that says "One of the parameters of a binary operator must be the containing type".
No, and this would be horrible. Users using your library would suddenly get different behaviors from their double variables!
You can write and use a wrapper object however:
public struct MyDouble
{
public double Value {get; set;}
public MyDouble(double initValue)
{
Value = initValue;
}
public static double operator +(MyDouble x, MyDouble y){
return Math.Round(x.Value + y.Value)
}
}
You can also make it castable to/from a double, among other options. This way users know they are using your object and won't be surprised when their math operations are rounded.
If you want to assign from a simple double, you would need to define an implicit operator, similar to that of Nullable<T> (source):
public static implicit operator MyDouble(double value) {
return new MyDouble(value);
}
You can't overload operators on primitive types. This would cause havoc in your codebase.
What you can do instead, is to create a simple wrapper around the primitive type, let's say RoundedDouble:
public struct RoundedDouble : IEquatable<RoundedDouble>, IComparable<RoundedDouble>
{
public readonly double Value;
public RoundedDouble(double value)
{
Value = Math.Round(value); // Or anything else
}
public static implicit operator RoundedDouble(double value)
{
return new RoundedDouble(value);
}
public static implicit operator double(RoundedDouble wrapper)
{
return wrapper.Value;
}
public int GetHashCode()
{
return Value.GetHashCode();
}
public bool Equals(object other)
{
if (other is RoundedDouble)
return ((RoundedDouble)other).Value == Value;
return false;
}
public string ToString()
{
return Value.ToString();
}
// Add your operators here, and implement the interfaces
}
This is a structure. It has the same value semantics as a double.
Extend it by adding the operators, and by implementing at least IEquatable<RoundedDouble> and IComparable<RoundedDouble>.
For example, if I have an object such as:
public class MyObject
{
public MyObject(int initialValue)
{
this.InitialValue = initialValue;
this.CurrentValue = initialValue;
}
public int InitialValue { get; set; }
public int CurrentValue { get; set; }
public static implicit operator MyObject(int someValue)
{
MyObject result = new MyObject(someValue);
return result;
}
}
Would it be possible to, in the implicit cast, keep the initial value if there was one and only update the current value?
The idea would be to do something like this:
MyObject test = 4; // Both InitialValue and CurrentValue are now 4.
test = 5; // InitialValue is 4 but CurrentValue is now 5.
It's a long shot and I don't think it would be possible but if anyone out there has any brilliant ideas to achieve this I'd appreciate it.
Thanks!
You can cast without making any assignment. One example of this would be when calling a function:
void SomeFunction(MyObject passedValue) { /* ... */ }
Could be called via your implicit cast like this:
SomeFunction(5);
And no assignment ever takes place.
Even when assignments do occur, remember that you assign to variables, not to objects. In a sense, the object you're asking for in this case is really the result variable.
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;
}
}
let's say I have a list of decimals :
List<decimal> values;
and 2 function to display a decimal :
string DisplayPct(decimal pct)
{
return pct.ToString("0.00 %");
}
string DisplayValue(decimal val)
{
return val.ToString("0.00");
}
What would be the best mechanism to implement so I could know which function to call depending on the value?
I would have liked to have for instance typedefs in C#. That way, I could have declared a type Percent and a type Decimal that would both represent decimal values, but then I could know how to display the value based on its type.
Any equivalent in C# ?
Thanks
Here are my classes :
public class Percent
{
public decimal value;
public Percent(decimal d) { value = d; }
public static implicit operator Percent(decimal d) { return new Percent(d); }
public static implicit operator decimal(Percent p) { return p.value; }
}
public class DecimalPrecise
{
public decimal value;
public DecimalPrecise(decimal d) { value = d; }
public static implicit operator DecimalPrecise(decimal d) { return new DecimalPrecise(d); }
public static implicit operator decimal(DecimalPrecise d) { return d.value; }
}
Wrap percent in a class. A bit of work on your part. Just make sure to define the implicit operator to capture decimals, and some of the other operations and ToString as you require.
It sounds like you want two classes: a decimal and a percent. Each one will have a ToString that prints appropriately. If they both have the same interface, you can have a collection of both in a List using that common interface.