I want some idea to how implicitly convert nullable "?" variables to district ones.
given this example
int? x = 5;
int y = x; //this gonna fail, !!!
i need some way to override = parameter, but unfortunately the = parameter is not overloadable... any suggestions
I'm using C#
You have two options, access the value directly (if you know for sure it's not null):
int y = x.Value;
or, use the null coalescing operator:
int y = x ?? 0; // 0 if null...
It is possible to implement an implicit cast operator, but only to or from types you define. For example, doing something like this..
public class NullableExtensions
{
public static implicit operator int(int? value)
{
return value ?? default(int);
}
}
.. will return a CS0556 compile error because the cast doesn't include the user-defined type.
The closest you could do is define your own Nullable type that does contain an implicit cast operator:
public struct ImplicitNullable<T> where T: struct
{
public bool HasValue { get { return this._value.HasValue; } }
public T Value { get { return this._value.Value; } }
public ImplicitNullable(T value) : this() { this._value = value; }
public ImplicitNullable(Nullable<T> value) : this() { this._value = value; }
public static implicit operator ImplicitNullable<T>(T value) { return new ImplicitNullable<T>(value); }
public static implicit operator ImplicitNullable<T>(Nullable<T> value) { return new ImplicitNullable<T>(value); }
public static implicit operator T(ImplicitNullable<T> value) { return value._value ?? default(T); }
public static implicit operator Nullable<T>(ImplicitNullable<T> value) { return value._value; }
private Nullable<T> _value { get; set; }
// Should define other Nullable<T> members, especially
// Equals and GetHashCode to avoid boxing
}
Note that although it's possible to write this code, it will likely lead to hard to trace bugs. I would recommend using an explicit cast, or throwing an exception when the value is null.
Afterwards, you can cast to and from as expected:
static void Main()
{
int myInt = 1;
int? nullableInt = 2;
ImplicitNullable<int> implicitInt;
// Convert from int or int?
implicitInt = myInt;
implicitInt = nullableInt;
// Convert to int or int?
myInt = implicitInt;
nullableInt = implicitInt;
}
Wait, I'm so confused...
Why don't you just use GetValueOrDefault?
I'm assuming this is C#.
You need to either cast, or use .value:
int? x = 5;
int y;
if(x.HasValue)
y = x.Value;
else
throw new//... handle error or something
Related
I have a very simple class:
public class MyCustomBoolean {
private bool _value = false;
public MyCustomBoolean(bool value) {
_value = value;
}
public bool value => _value;
#region casting support
public static explicit operator string(MyCustomBoolean m) {
return m.value.ToString();
}
public static explicit operator bool(MyCustomBoolean m) {
return m.value;
}
#endregion
}
And now, somewhere in my code I try to:
public void someMethod(MyCustomBoolean param) {
string testString = param;
}
The error I keep getting is:
cannot convert source type MyCustomBoolean to type string
I have a few classes handling different types but this one is the only one causing me trouble.
What am I doing wrong here?
You're attempting to use an explicit operator as an implicit one.
The following should work:
public void someMethod(MyCustomBoolean param) {
string testString = (string)param; // explicit cast to string
}
If you wanted to use the code the way it was written, you would need to instead define conversion operators as implicit, like so:
public static implicit operator string(MyCustomBoolean m) {
return m.value.ToString();
}
public static implicit operator bool(MyCustomBoolean m) {
return m.value;
}
At which point, your previous code will work as expected.
public void someMethod(MyCustomBoolean param) {
string testString = param; // implicit cast
}
I have the following class:
public class InterlockedBool
{
private int _value;
public bool Value
{
get { return _value > 0; }
set { System.Threading.Interlocked.Exchange(ref _value, value ? 1 : 0); }
}
public static bool operator ==(InterlockedBool obj1, bool obj2)
{
return obj1.Value.Equals(obj2);
}
public static bool operator !=(InterlockedBool obj1, bool obj2)
{
return !obj1.Value.Equals(obj2);
}
public override bool Equals(bool obj)
{
return this.Value.Equals(obj);
}
}
My question is: Can I check if Value is true, without == true? The operator override works, but can I also use it like so?
InterlockedBool ib = new InterlockedBool();
if (ib) { }
Instead of (this works, but normally I omit the == true in if statements.
if (ib == true) { }
And how do I assign it to a value without use .Value =?
Thanks for you help :)
You need to be able to convert your object to and from a boolean
Implicit Conversion
Your object to a boolean:
public static implicit operator bool(InterlockedBool obj)
{
return obj.Value;
}
Then a boolean to your object:
public static implicit operator InterlockedBool(bool obj)
{
return new InterlockedBool(obj);
}
Then you can test it:
InterlockedBool test1 = true;
if (test1)
{
//Do stuff
}
Explicit Conversion
If you want the users of this class to be aware that there is a conversion happening, you can force an explicit cast :
public static explicit operator bool(InterlockedBool obj)
{
return obj.Value;
}
public static explicit operator InterlockedBool(bool obj)
{
return new InterlockedBool(obj);
}
Then you must explicitly cast your objects:
InterlockedBool test1 = (InterlockedBool)true;
if ((bool)test1)
{
//Do stuff
}
EDIT (due to OP comment)
In the conversion from boolean to your object, I call a constructor that you did not mention, here is how I would build it:
public InterlockedBool(bool Value)
{
this.Value = Value;
}
Therefore the setting of the value is guranteed thread-safe
You can define an implicit conversion to bool :
public static implicit operator bool(InterlockedBool obj)
{
return obj.Value;
}
public struct DecimalOrNaN
{
public decimal Value;
public bool isNaN;
public DecimalOrNaN (double D)
{
if (Double.IsNaN(D))
{
Value = default(decimal);
isNaN = true;
}
else
{
Value = (decimal)D;
isNaN = false;
}
}
public DecimalOrNaN(decimal D)
{
Value = D;
isNaN = false;
}
public implicit operator DecimalOrNaN(double D)
{
return new DecimalOrNaN(D);
}
public implicit operator DecimalOrNaN(decimal D)
{
return new DecimalOrNaN(D);
}
public DecimalOrNaN operator *(int I, DecimalOrNaN D)
{
return new DecimalOrNaN(D.Value * I);
}
}
I have this struct (let's just call it DON) here which stores decimals, but has an option to have "Not a Number" in it, which regular decimal lacks. I can add the needed implicit conversions myself, but i also need it to be able to add, subtract and multiply with other DONs as well as with ints, doubles and decimals. Do I have to create each operator with each variation of parameters (int + DON, DON + int, int * DON,DON * int and so on) myself or is there a better way of doing it?
My suggestion would be to use the nullable type: decimal?. This will allow you to assign NULL to the variable to indicate it's not a number.
Documentation for this feature of the language is available here: http://msdn.microsoft.com/en-us/library/1t3y8s4s.aspx
I am trying to write a function to convert the contents of a string "12345" to an int.
If the string is blank i would like to return null (uninitialized), not the value 0.
Problem is, functions do not return un-initialized values.
My code will not compile as Retval can return an uninitialized value......
My attempt so far:
public int ConvertStringToNumber(String TheString)
{
// Uninitialized
int Retval;
if (TheString.Length > 0)
{
// We have a valid string
if (Int32.TryParse(TheString, out Retval))
{
// We have a valid Number
}
}
// Return the number or null
return Retval;
}
Can you use Nullable int ? it will allow set as nullable . See here : http://www.codeproject.com/Articles/11854/C-2-0-Nullable-Types
You can use a nullable int (more info here).
Nullable types can represent all the values of an underlying type, and
an additional null value.
public int? ConvertStringToNumber(String TheString)
{
int retval;
bool isInt = Int32.TryParse(TheString, out retval);
return isInt ? retval : null;
}
Note: When using nullable types, you'll need to use a cast or get it's value. See here.
Example:
int? n = ConvertStringToNumber("123");
int value = n.Value;
// or
int value = (int)n;
If you assigned a value to the Retval object AT THE FIRST TIME, then the value is valid in THAT area ONLY.
So, Retval is null when you return it.
since Int32.TryParse(TheString, out Retval) require int type not nullable
public int? ConvertStringToNumber(String TheString)
{
// Uninitialized
int Retval;
if (TheString.Length > 0)
{
// We have a valid string
if (Int32.TryParse(TheString, out Retval))
{
// We have a valid Number
return Retval;
}
}
// Return the number or null
return null;
}
Simple extension method to resolve your problem
using System;
namespace temp
{
class Program
{
static void Main(string[] args)
{
string valu = "";
Console.WriteLine(valu.ToInt32());
Console.ReadLine();
}
}
public static class MyExtentions
{
public static int ToInt32(this string s)
{
int x;
if (s != null)
{
if (s.Length > 1)
x = Convert.ToInt32(s);
else
x = 0;
}
else
{
x= 0;
}
return x;
}
}
}
int? x = ConvertStringToNumber("1");
int value = x.Value;
String to numeric conversion in c#
I created a struct
public struct MyCalender : IComparable<MyCalender>
{
public int CompareTo(PersianDate other)
{
return DateTime.Compare(this, other);
}
.
.
.
.
.
}
I new two object of this in a other UserControl, and i want compare they.
I use this code but i get error.
MyCalender value = new MyCalender(2010,11,12);
MyCalender value2 = new MyCalender(2010,11,12);
if (value < value2) ==> geterror
IComparable exposes CompareTo. < and > must be overloaded separately:
class Foo : IComparable<Foo>
{
private static readonly Foo Min = new Foo(Int32.MinValue);
private readonly int value;
public Foo(int value)
{
this.value = value;
}
public int CompareTo(Foo other)
{
return this.value.CompareTo((other ?? Min).value);
}
public static bool operator <(Foo a, Foo b)
{
return (a ?? Min).CompareTo(b) < 0;
}
public static bool operator >(Foo a, Foo b)
{
return (a ?? Min).CompareTo(b) > 0;
}
}
I edited the code so that it does not fail when comparing against null. To keep it brief I used a shortcut that works unless value is Int32.MinValue for a proper Foo. Strictly speaking you'd have to check for null explicitly to get the contract right:
By definition, any object compares greater than (or follows) null, and
two null references compare equal to each other.
Besides, implementing IComparable<T> means that CompareTo(T value) takes a parameter of T. Therefore MyCalendar : IComparable<MyCalender> should implement a method CompareTo(MyCalendar other) rather than PersianDate (or implement IComparable<PersianDate>).
You should either use CompareTo method that you already implemented instead of > in the line you posted or you need to overload > and < operators for your specific class. For instance:
public static bool operator >(MyCalendar c1, MyCalendar c2)
{
return c1.CompareTo(c2) > 0;
}
public static bool operator <(MyCalendar c1, MyCalendar c2)
{
return c1.CompareTo(c2) < 0;
}
But keep in mind that you have to overload both of them.
if comparing just a datetime object,
would something like
DateTime A = DateTime.Now, B = DateTime.Now.AddMinutes(1);
var isqual = A.Date.CompareTo(B.Date);
do the trick?
or something like:
class Calender
{
public DateTime datetime { get; set;}
}
class DateComparer : Calender, IComparable<Calender>
{
public int CompareTo(Calender other)
{
return other.datetime.Date.CompareTo(this.datetime.Date);
}
}