overloadingg operator

Marco

Hello, I have this problem:

class Person {
    string name;
    string surname;
    public static bool operator ==(Person p1, Person p2)
    {
            if (p1.name == p2.name && p1.surname == p2.surname) return true;else return false;
     }
}

//main program..
   Person p = p.Mysearch("Tim"); // if it don't found Tim, Mysearch() return null
   if (p == null) { ......} //problem is here

The problem is when I check for p ==null; I have defined == the check p.name and p.surname but null HASN'T any attribute (it isn't a person...

How can I solve it problem??
thanks.

3 Replies

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Alan19y ago
If you recode that line as follows, then no exception will be thrown if p1 is null, whether you've overloaded the != operator or not:

if (p1 != null && p1.isNotProfessor()) listperson.Add(p1);
Marco19y ago
Hello I just have a similar problem. Can I solve with operator overloading?

if ( p1.isNotProfessor()) listperson.Add(p1);

Sometimes happen that p1 comes "null": so the code on the if crash at runtime.
Can I solve it ? thanks.
Alan19y ago
To avoid the == operator being called recursively, you need to use the static Object.ReferenceEquals() method to test for null.

You also need to override the != operator and, to get rid of the compiler wanrings that will otherwise come up, you should override the Object.Equals() and Object.GetHashCode() methods as well. Something like this:

    public static bool operator ==(Person p1, Person p2)
    {
       if (Object.Equals(p1, null))
          return (Object.ReferenceEquals(p2, null));
       else if (Object.ReferenceEquals(p2,null))
          return (Object.ReferenceEquals(p1,null));
       else if (p1.name == p2.name && p1.surname == p2.surname)
          return true;
       else
          return false;
    }

    public static bool operator !=(Person p1, Person p2)
    {
        return !(p1 == p2);
    }

    public override bool Equals(object obj)
    {
        if (!(obj is Person))
           return false;
        return (this == (Person)obj);
    }

    public override int GetHashCode()
    {
        return base.GetHashCode();
    }