运算符重载等于

我已经看过 有个问题了

我明白，这是必要的实施 ==，!=和 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);
}
}

我假设，我已经正确地编写了代码来覆盖 ==、 !=、 Equals操作符。

'myNameSpace.BOX.Equals(myNameSpace.BOX)' is marked as an override
but no suitable method found to override.

因此，问题是-如何覆盖以上操作符和摆脱这个错误？

135938 次浏览
小开
最佳答案

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>.

小开

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.Equals(obj2);
}
public static bool operator !=(Box obj1, Box obj2) => !(obj1 == obj2);
public bool Equals(Box other)
{
if (ReferenceEquals(other, null))
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) => Equals(obj as Box);


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.

小开

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

小开 
public class BOX
{
double height, length, breadth;


public static bool operator == (BOX b1, BOX b2)
{
if (b1 is null)
return b2 is 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)
return false;


return obj is BOX b2? (length == b2.length &&
breadth == b2.breadth &&
height == b2.height): false;


}


public override int GetHashCode()
{
return (height,length,breadth).GetHashCode();
}
}

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