I've already gone through question
I understand that, it is necessary to implement ==, != and Equals().
public class BOX
{
double height, length, breadth;
// this is first one '=='
public static bool operator== (BOX obj1, BOX obj2)
{
return (obj1.length == obj2.length
&& obj1.breadth == obj2.breadth
&& obj1.height == obj2.height);
}
// this is second one '!='
public static bool operator!= (BOX obj1, BOX obj2)
{
return !(obj1.length == obj2.length
&& obj1.breadth == obj2.breadth
&& obj1.height == obj2.height);
}
// this is third one 'Equals'
public override bool Equals(BOX obj)
{
return (length == obj.length
&& breadth == obj.breadth
&& height == obj.height);
}
}
I assume, I've written code properly to override ==,!=,Equals operators. Though, I get compilation errors as follows.
'myNameSpace.BOX.Equals(myNameSpace.BOX)' is marked as an override
but no suitable method found to override.
So, question is - How to override above operators & get rid of this error?
I think you declared the Equals method like this:
public override bool Equals(BOX obj)
Since the object.Equals method takes an object, there is no method to override with this signature. You have to override it like this:
public override bool Equals(object obj)
If you want type-safe Equals, you can implement IEquatable<BOX>.
As Selman22 said, you are overriding the default object.Equals method, which accepts an object obj and not a safe compile time type.
In order for that to happen, make your type implement IEquatable<Box>:
public class Box : IEquatable<Box>
{
double height, length, breadth;
public static bool operator ==(Box obj1, Box obj2)
{
if (ReferenceEquals(obj1, obj2))
{
return true;
}
if (ReferenceEquals(obj1, null))
{
return false;
}
if (ReferenceEquals(obj2, null))
{
return false;
}
return (obj1.length == obj2.length
&& obj1.breadth == obj2.breadth
&& obj1.height == obj2.height);
}
// this is second one '!='
public static bool operator !=(Box obj1, Box obj2)
{
return !(obj1 == obj2);
}
public bool Equals(Box other)
{
if (ReferenceEquals(null, other))
{
return false;
}
if (ReferenceEquals(this, other))
{
return true;
}
return height.Equals(other.height)
&& length.Equals(other.length)
&& breadth.Equals(other.breadth);
}
public override bool Equals(object obj)
{
if (ReferenceEquals(null, obj))
{
return false;
}
if (ReferenceEquals(this, obj))
{
return true;
}
return obj.GetType() == GetType() && Equals((Box)obj);
}
public override int GetHashCode()
{
unchecked
{
int hashCode = height.GetHashCode();
hashCode = (hashCode * 397) ^ length.GetHashCode();
hashCode = (hashCode * 397) ^ breadth.GetHashCode();
return hashCode;
}
}
}
Another thing to note is that you are making a floating point comparison using the equality operator and you might experience a loss of precision.
In fact, this is a "how to" subject. So, here is the reference implementation:
public class BOX
{
double height, length, breadth;
public static bool operator == (BOX b1, BOX b2)
{
if ((object)b1 == null)
return (object)b2 == null;
return b1.Equals(b2);
}
public static bool operator != (BOX b1, BOX b2)
{
return !(b1 == b2);
}
public override bool Equals(object obj)
{
if (obj == null || GetType() != obj.GetType())
return false;
var b2 = (BOX)obj;
return (length == b2.length && breadth == b2.breadth && height == b2.height);
}
public override int GetHashCode()
{
return height.GetHashCode() ^ length.GetHashCode() ^ breadth.GetHashCode();
}
}
REF: https://msdn.microsoft.com/en-us/library/336aedhh(v=vs.100).aspx#Examples
UPDATE: the cast to (object) in the operator == implementation is important, otherwise, it would re-execute the operator == overload, leading to a stackoverflow. Credits to @grek40.
This (object) cast trick is from Microsoft String == implementaiton.
SRC: https://github.com/Microsoft/referencesource/blob/master/mscorlib/system/string.cs#L643
