# Equals and GetHashCode

suggest changeEach implementation of `Equals`

must fulfil the following requirements:

**Reflexive**: An object must equal itself.`x.Equals(x)`

returns`true`

.**Symmetric**: There is no difference if I compare x to y or y to x - the result is the same.`x.Equals(y)`

returns the same value as`y.Equals(x)`

.**Transitive**: If one object is equal to another object and this one is equal to a third one, the first has to be equal to the third.if`(x.Equals(y) && y.Equals(z))`

returns`true`

, then`x.Equals(z)`

returns`true`

.**Consistent**: If you compare an object to another multiple times, the result is always the same.Successive invocations of`x.Equals(y)`

return the same value as long as the objects referenced by x and y are not modified.**Comparison to null**: No object is equal to`null`

.`x.Equals(null)`

returns`false`

.

Implementations of `GetHashCode`

:

**Compatible with**

: If two objects are equal (meaning that**Equals**`Equals`

returns true), then`GetHashCode`

**must**return the same value for each of them.**Large range**: If two objects are not equal (`Equals`

says false), there should be a**high probability**their hash codes are distinct.*Perfect*hashing is often not possible as there is a limited number of values to choose from.**Cheap**: It should be inexpensive to calculate the hash code in all cases.

See: Guidelines for Overloading Equals() and Operator ==

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