c# - Is it possible to write a hash code function for an comparer that matches many-to-many? -

can write hash code function following comparer logic?

two instances of my equal if @ least 2 properites (a, b, c) match.

the equals part simple, i'm stumped on hash code part, , part of me thinking might not possible.

class myothercomparer : iequalitycomparer<my> {     public bool equals(my x, y)     {         if (object.referenceequals(x, y))              return true;                if (object.referenceequals(x, null) || object.referenceequals(y, null))              return false;          int matches = 0;          if(x.a == y.a) matches++;          if(x.b == y.b) matches++;          if(x.c == y.c) matches++;          // match on 2 out of 3         return  (matches > 1)     }      // if equals() returns true pair of objects      // gethashcode() must return same value these objects.     public int gethashcode(my x)     {        // ???     } } 

update: in addition correct answer reed copsey, important point general usefulness of fuzzy comparer stated ethan brown - please see answer full understanding of underlies question/answer.

yes, it's possible. simplest implementation return constant.

public int gethashcode(my x)  {     return 0; } 

the gethashcode documentation states:

implementations required ensure if equals method returns true 2 objects x , y, value returned gethashcode method x must equal value returned y.

however, free return same hash code 2 objects not equal, well.

that being said, potentially cause algorithms perform poorly, you'll lots of hash collisions. however, given nature of odd/unique equality check, may required.

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note going problematic in case. given logic, it's possible have 3 objects, comparer.equals(foo, bar)==true , comparer.equals(foo, baz)==true comparer.equals(baz, bar)==false. problematic in many cases iequalitycomparer<t> used.