I am at a brick wall here. Is it possible to copy one bool to the ref of another. Consider this code . . .
bool a = false;
bool b = a;
b is now a totally separate bool with a value of false. If I subsequently change a, it will have no effect on b. Is it possible to make a = b by ref? How would I do that?
Many thanks
No. Since bool is a value type, it will always be copied by value.
The best option is to wrap your bool within a class - this will give it reference type semantics:
public class BoolWrapper
{
public bool Value { get; set; }
public BoolWrapper (bool value) { this.Value = value; }
}
BoolWrapper a = new BoolWrapper(false);
BoolWrapper b = a;
b.Value = true;
// a.Value == true
Thanks to #Reed for his answer (+1)! He encouraged me to a more "generic" solution! :)
public class ValueWrapper<T> where T : struct
{
public T Value { get; set; }
public ValueWrapper(T value) { this.Value = value; }
}
Small extension to Andrey's answer... this allows you to assign it to whatever type you want in the end directly. So:
ValueWrapper<bool> wrappedBool = new ValueWrapper<bool>(true);
bool unwrapped = wrappedBool; // you can assign it direclty:
if (wrappedBool) { // or use it how you'd use a bool directly
// ...
}
public class ValueWrapper<T>
{
public T Value { get; set; }
public ValueWrapper() { }
public ValueWrapper(T value) {
this.Value = value;
}
public static implicit operator T(ValueWrapper<T> wrapper)
{
if (wrapper == null) {
return default(T);
}
return wrapper.Value;
}
}
this may not be what you want, but if your scenario were such that you wanted a function that you called to modify your local boolean, you can use the ref or out keyworkd.
bool a = false;
F(ref a);
// a now equals true
...
void F(ref bool x)
{
x = true;
}
So I'm guessing you are needing to pass a reference a bool, that you cannot wrap with a 'BoolWrapper' class, because the bool lives some place that you cannot or do not wish to modify.
It can be done!
First declare what any bool reference will look like
/// <summary> A reference to a bool.</summary>
/// <param name="value">new value</param>
/// <returns>Value of boolean</returns>
public delegate bool BoolRef(bool? value = null);
Now you can make a reference to myBool like this
bool myBool; // A given bool that you cannot wrap or change
private bool myBoolRef(bool? value) {
if (value != null) {
myBool = (bool)value;
}
return myBool;
}
And use it like this:
void myTestCaller() {
foo(myBoolRef);
}
void foo(BoolRef b) {
bool c = b(); // get myBool
b(true); // set myBool to true
}
The same trick works for other value types such as int
A bool is a value type and cannot be copied by reference.
I had a case where I wanted one class to change another class' bool - please note that there are better ways to handle this situation but this is a proof of concept using Actions.
public class Class1
{
bool myBool { get; set; }
void changeBoolFunc(bool val) { myBool = val; }
public Class1()
{
Action<bool> changeBoolAction = changeBoolFunc;
myBool = true;
Console.WriteLine(myBool); // outputs "True"
Class2 c2 = new Class2(changeBoolAction);
Console.WriteLine(myBool); // outputs "False"
}
}
public class Class2
{
public Class2(Action<bool> boolChanger) { boolChanger(false); }
}
void Main()
{
Class1 c1 = new Class1();
}
Just use the flags as Nullable<bool> or bool? and set those in the struct that's passed to the generic method. The ValueWrapper<T> class above is essentially exactly what Nullable<T> does.
Related
I want to make a struct that when its value is set, you can call the value by the variable name.
struct A
{
int Value;
}
Main()
{
// Sets Value to 9
A Number = 9;
Console.Write(Number);
// output should be 9
}
I expect the output to be 9
You can optimize your code like this:
struct A
{
public int Value;
public A(int val)
{
Value = val;
}
public override string ToString()
{
return Value.ToString();
}
}
and use like you wanted:
// Sets Value to 9
A Number = new A(9);
Console.Write(Number);
To use exactly what you wrote A number = 9; Console.Write(Number); you first need to define an implicit assignment operator, and then you need to override the ToString() method to get the right output. Sample code:
struct A
{
public int Value;
public A(int value)
{
Value = value;
}
// This allows creating an instance of struct A by writing it as an assignment statement
static public implicit operator A(int value)
{
return new A(value);
}
public override string ToString()
{
return Value.ToString();
}
}
public static void Main()
{
A Number = 9;
Console.Write(Number);
}
Live demo here: https://dotnetfiddle.net/WZPsLX
Your struct misses accessors for Value
struct A
{
public int Value { get; set; }
}
Main()
{
A number = new A();
number.Value = 9;
Console.WriteLine(number.Value)
}
Adding to Peter B's answer, you could also define the opposite implicit conversion instead of ToString()
public static implicit operator int(A a)
{
return a.Value;
}
Is it possible to somehow use this class(test.Value is not what i'm looking for):
RefBool test = false;
if (test)
{
}
This is class body:
public class RefBool
{
public bool Value { get; set; }
public RefBool(bool value)
{
this.Value = value;
}
public static implicit operator RefBool(bool val)
{
return new RefBool(val);
}
}
Yes, if you overload the true and false operators:
// note: you might want to think about what `null` means in terms of true/false
public static bool operator true(RefBool val) => val.Value;
public static bool operator false(RefBool val) => !val.Value;
I'm not sure it is a good idea, though; ref bool seems more obvious.
Is there anyway to make is so that I can say something like
if(boolClass) {}
Where the boolClass is calling a contained function. Kinda like an overloaded bool operator or something.
Thanks for any help.
There is actually a 'true' operator you can use for this purpose, though it's a bit obscure. This is slightly more specific than a conversion to bool, as it is limited to use in expressions that check for true/false.
public class BoolClass
{
public static bool operator true(BoolClass instance)
{
return true; //Logic goes here
}
public static bool operator false(BoolClass instance)
{
return true; //Logic goes here
}
public void Test()
{
BoolClass boolClass = new BoolClass();
if (boolClass)
{
//Do something here
}
}
}
Note that MS actually recommends against using this operator,as it was originally intended to allow for a kind of nullable bool type (where a value could be neither true nor false). Since nullable bools are now natively supported, those are preferred. I'd recommend against using it in production code, mainly because most developers won't be familiar with the syntax, causing confusion.
My first point would be to caution you against this, usually you want to use the bool or bool? classes available directly or indirectly.
If you are certain that is what you need, then you will need an implicit conversion operator to bool
//In the definition of boolClass
public static implicit operator bool(boolClass obj)
{
//Return a bool in this method
}
You can use a implicit operator to convert your class to a Boolean.
This is a full and simple example :
Classe
using System;
namespace TestLogic
{
internal class FuzzyLogic
{
public FuzzyLogic(Double init)
{
this.value = init;
}
public Double value { get; private set; }
public static implicit operator Boolean(FuzzyLogic logic)
{
return logic.value < 0.1;
}
}
}
Using the convertion
using System;
namespace TestLogic
{
internal class Program
{
private static void Main(string[] args)
{
FuzzyLogic logic = new FuzzyLogic(0.2);
if (logic)
{
Console.WriteLine("It's true !");
}
else
{
Console.WriteLine("It's not true !");
}
Console.ReadLine();
}
}
}
Sounds like a property:
public bool boolClass
{
get { return false; } // or a calculated boolean value
}
You can invoke it exactly like you asked about from inside the same class:
if(boolClass) {}
Add a conversion operator to your class. Example (ideone):
using System;
public class A
{
private int i;
public int I { get { return i; } }
public A(int i) { this.i = i; }
public static implicit operator bool(A a) { return a.i != 0; }
}
public class Test
{
public static void Main()
{
A a1 = new A(0);
if (a1)
Console.WriteLine("a1 is true");
else
Console.WriteLine("a1 is false");
A a2 = new A(42);
if (a2)
Console.WriteLine("a2 is true");
else
Console.WriteLine("a2 is false");
}
}
Output:
a1 is false
a2 is true
I have defined the following interface:
public interface IHaveAProblem
{
string Issue { get; set; }
}
And here is the implementation of IHaveAProblem:
public class SomeProblem : IHaveAProblem
{
public string Issue { get; set; }
public override bool Equals(object obj)
{
SomeProblem otherObj = obj as SomeProblem;
if (otherObj == null)
{
return false;
}
return this.Issue == otherObj.Issue;
}
public override int GetHashCode()
{
return base.GetHashCode();
}
public static bool operator ==(SomeProblem rhs, SomeProblem lhs)
{
// Null check
if (Object.ReferenceEquals(rhs, null) || Object.ReferenceEquals(lhs, null))
{
if (Object.ReferenceEquals(rhs, null) && Object.ReferenceEquals(lhs, null))
{
// Both are null. They do equal each other
return true;
}
// Only 1 is null the other is not so they do not equal
return false;
}
return rhs.Equals(lhs);
}
public static bool operator !=(SomeProblem rhs, SomeProblem lhs)
{
// Null check
if (Object.ReferenceEquals(rhs, null) || Object.ReferenceEquals(lhs, null))
{
if (Object.ReferenceEquals(rhs, null) && Object.ReferenceEquals(lhs, null))
{
// Both are null. They do equal each other
return false;
}
// Only 1 is null the other is not so they do not equal
return true;
}
return !rhs.Equals(lhs);
}
}
When I use the object, I can get the correct results for the == compare:
SomeProblem firstTest = new SomeProblem()
{
Issue = "Hello World"
};
SomeProblem secondTest = new SomeProblem()
{
Issue = "Hello World"
};
// This is true
bool result = firstTest == secondTest;
However, when I try to compare the interfaces, it is doing a memory compare rather than the operator == on SomeProblem:
IHaveAProblem firstProblem = new SomeProblem()
{
Issue = "Hello World"
};
IHaveAProblem secondProblem = new SomeProblem()
{
Issue = "Hello World"
};
Is it possible to have the interface use the == on SomeProblem rather than a memory compare?
I know I can do a firstProblem.Equals(secondProblem) and get the proper results. However, I am creating a framework and I will not know how it is used in the end. I thought == would work correctly.
The operator == is static. You cannot define static methods for interfaces in C#. Also, for all operators at least one of the argument types needs to be of the same type as the class it is defined in, therefore: No operator overloading for interfaces :(
What you CAN do is use an abstract class instead - and define the operator there. Again, the operator may NOT be virtual (since static methods cannot be virtual...)
[Edited, reason see comment.]
I konw, this is an old question, but all examples provided show how to compare two class instances, and no one points out how to compare two interface instances.
In some cases, this is the DRYest way to compare interfaces.
public interface IHaveAProblem
{
string Issue { get; set; }
}
public class IHaveAProblemComparer : IComparer<IHaveAProblem>, IEqualityComparer<IHaveAProblem>
{
public int Compare(IHaveAProblem x, IHaveAProblem y)
{
return string.Compare(x.Issue, y.Issue);
}
public bool Equals(IHaveAProblem x, IHaveAProblem y)
{
return string.Equals(x.Issue, y.Issue);
}
public int GetHashCode(IHaveAProblem obj)
{
return obj.GetHashCode();
}
}
Usage?
IHaveAProblemComparer comparer = new IHaveAProblemComparer();
List<IHaveAProblem> myListOfInterfaces = GetSomeIHaveAProblemObjects();
myListOfInterfaces.Sort(comparer); // items ordered by Issue
IHaveAProblem obj1 = new SomeProblemTypeA() { Issue = "Example1" };
IHaveAProblem obj2 = new SomeProblemTypeB() { Issue = "Example2" };
bool areEquals = comparer.Equals(obj1, obj2); // False
IIRC (and I could be wrong here), C# interfaces don't allow operator overloading.
But in this case that's okay. The == operator normally maps to reference equality. It sounds like you want value equality, and that means you want to force them to override the .Equals() (and consequently also .GetHashCode()) functions. You do that by having your interface inherit from IEquatable.
Have you tried implementing IComparable?
Like this:
public interface IHaveAProblem : IComparable
{
string Issue { get; set; }
}
And then in the implementation of the class:
public class SomeProblem : IHaveAProblem
{
public string Issue { get; set; }
...
public int CompareTo(object obj)
{
return Issue.CompareTo(((SomeProblem)obj).Issue);
}
}
Note that, this works only when you compare two instances of SomeProblem, but not any other implementations of the IHaveAProblem interface.
Not sure if there could occur a NullReferenceException.
I have a custom object that maps a boolean value from a legacy database to a C# bool (and back again).
My custom bool object looks like this:
public class S2kBool : IUserDefinedType {
public bool Value { get; set; }
public Type SupportedType { get { return typeof(string); } }
// These are the values used to represent booleans in the database
public const string TrueValue = "Y";
public const string FalseValue = "N";
public static S2kBool True {
get { return new S2kBool(true); }
}
public static S2kBool False {
get { return new S2kBool(false); }
}
public S2kBool() : this(false) { }
public S2kBool(bool value) {
this.Value = value;
}
// Called when a property of this type is populated from the database
public void FromSimpleDataType(object value) {
this.Value = value.ToString() == TrueValue;
}
// Called when a property of this type is inserted into the database
public object ToSimpleDataType() {
return this.Value ? TrueValue : FalseValue;
}
}
I would like to be able to do something like this:
public class TestObject {
public S2kBool IsActive = S2kBool.True;
}
TestObject tObj = new TestObject();
if (tObj.IsActive == S2kBool.True) {
// the above would evaluate to true
}
I've seen a few different methods for doing comparisons between objects, but I'm not sure of which one to use.
EDIT: Better yet, would it be possible to do something like the following and have C# treat the S2kBool object as an actual Boolean during comparison? It should also allow comparisons with other S2kBool objects, as well.
if (tObj.IsActive == true) { ... }
There are 2 things to look at; an implicit conversion operator (in S2kBool) to bool, or the true/false operators themselves...
true/false operators (note I prefer the implicit bool conversion myself):
public static bool operator true(S2kBool x) {
return x.Value;
}
public static bool operator false(S2kBool x) {
return !x.Value;
}
then you can use if(tObj.IsActive)
conversion operator:
public static implicit operator bool(S2kBool x) {
return x.Value;
}
works likewise
You might also add a conversion in the other direction:
public static implicit operator S2kBool(bool x)
{
return new S2kBool(x);
}
Then you can assign IsActive = false; etc
Finally, I wonder if this should be an immutable struct? It might be confusing if you expect this to behave like a value. For example, look at the last line here:
TestObject obj1 = new TestObject(),
obj2 = new TestObject();
obj1.IsActive = obj2.IsActive = S2kBool.True;
Console.WriteLine(obj1.IsActive);
Console.WriteLine(obj2.IsActive);
obj1.IsActive.Value = false;
Console.WriteLine(obj1.IsActive);
Console.WriteLine(obj2.IsActive); // what does this print?
This prints false, because both IsActive fields point to the same instance of S2kBool. If that was the intent, then fine. But if it was me, I'd make it immutable (whether class or struct). But since it doesn't really have any state other than a bool, I'd argue that this fits well as a struct.
To be honest, I'm not entirely sure why it is needed at all, when all the functionality could be done via static methods / etc.
Yes, you can do that. You would need to define equality operators and override the Equals method.
Here is an article about operator overloading:
http://www.csharphelp.com/archives/archive135.html
Here is an example of a type with overridden equality operators. You can do the same with assignment and conversion operators, making your type work seamlessly with the built-in bool type. (I took your example, shortened it a bit to keep the example short, and added the equality operators).
public struct S2kBool : IEquatable<bool>
{
public bool Value { get; set; }
public bool Equals(bool other)
{
return Value == other;
}
public override int GetHashCode()
{
return Value.GetHashCode();
}
public static bool operator ==(bool left, S2kBool right)
{
return right.Equals(left);
}
public static bool operator !=(bool left, S2kBool right)
{
return !(left == right);
}
public static bool operator ==(S2kBool left, bool right)
{
return left.Equals(right);
}
public static bool operator !=(S2kBool left, bool right)
{
return !(left == right);
}
}