As stated in the System.HashCode documentation, adding together hashes returned by successive HashCode.Combine calls is NOT the solution. While the static HashCode.Combine method overloads only allow up to 8 values, these are just convenience methods – to combine more, instantiate the HashCode class itself and use it as follows: public override int GetHashCode() { HashCode … Read more
Using GetHashCode() is incorrect. You should cast to int. Using it the way you do is asking for raptors(or Raymond) to come and eat you. That GetHashCode() happens to return the integer value of the enum is an implementation detail and may change in future versions of .net. GetHashCode() guarantees that if two values are … Read more
According to documentation: If two string objects are equal, the GetHashCode method returns identical values. However, there is not a unique hash code value for each unique string value. Different strings can return the same hash code. Thus, some other effect must be in play for the two calls to give different results. One theory … Read more
If you use resharper it can generate the GetHashCode(), Equals and operator method bodies for you. Access this menu by pressing Alt+Insert. http://www.jetbrains.com/resharper/webhelp/Code_Generation__Equality_Members.html
Test that two distinct objects which are equal have the same hash code (for various values). Check that non-equal objects give different hash codes, varying one aspect/property at a time. While the hash codes don’t have to be different, you’d be really unlucky to pick different values for properties which happen to give the same … Read more
Why do hash codes for string change for every execution in .NET In short to prevent hash collision attacks. You can roughly find out the reason from the docs of the <UseRandomizedStringHashAlgorithm> configuration element: The string lookup in a hash table is typically an O(1) operation. However, when a large number of collisions occur, the … Read more
Obvious potential answer: because that will cost memory. There’s a cost/benefit analysis here: Cost: 4 bytes for every string (and a quick test on each call to GetHashCode). Also make the string object mutable, which would obviously mean you’d need to be careful about the implementation – unless you always compute the hash code up-front, … Read more
I’d do it the same way I normally combine hash codes – with an addition and a multiplication: public override int GetHashCode() { unchecked { int hash = 19; foreach (var foo in foos) { hash = hash * 31 + foo.GetHashCode(); } return hash; } } (Note that you shouldn’t add anything to the … Read more
Table of contents When do I override object.GetHashCode? Why do I have to override object.GetHashCode()? What are those magic numbers seen in GetHashCode implementations? Things that I would like to be covered, but haven’t been yet: How to create the integer (How to “convert” an object into an int wasn’t very obvious to me anyways). … Read more
Domain-Driven Design makes the distinction between Entities and Value Objects. This is a good distinction to observe since it guides how you implement Equals. Entities are equal if their IDs equal each other. Value Objects are equal if all their (important) constituent elements are equal to each other. In any case, the implementation of GetHashCode … Read more