Equals and GetHashCode and overriding them?

Question

C++ / C#

They say there is a rule that if we redefine Equals, then we must redefine GetHashCode - why?

Answer 1

First of all: to work correctly with hash collections (of the Dictionary type), namely, when used as a key. Their internal logic assumes that if for two objects Equalsreturns true, then the values ​​returned GetHashCodemust be equal. If this is not the case, then the collection will not work correctly: for example, it will not find values ​​by key, although they are there.