Should You Override GetHashCode When Overriding Equals in .NET?

.NET rewritten EQUALS should we rewrite Gethashcode?

When defining custom types in .NET, if necessary, not only should you rewrite the EQUALS method, but also rewrite the GethashCode method, which is very important. This is particularly important when the type is used as a key in a collection of dictionaries and hash sets.

Why rewritten Gethashcode?

Gethashcode is responsible for generating hash code for objects. Without custom comparators, collecting this hash code to determine the proper schedule of finding objects in it. If the hash code of the two objects is the same, it is assumed that they are located in the same bucket, and only at that time, Equals will be called to perform more detailed equal checks.

The preferred Gethashcode method

Considering the provided FOO class, the rewriting of Equals is compared based on the FOOID attribute. The first choice of Gethashcode is returned to FOOID. This method is consistent with Equals logic to ensure that objects with the same FOOID have the same hash code.

The consequences of incorrect rewriting Gethashcode

ignore the rewriting Gethashcode and use the default implementation, which will cause the following adverse effects:

Miss equal object: If the two objects are actually equal but have different hash codes, they may never be considered equal because they will not call Equals.

Too many conflicts:

Incorrect Gethashcode implementation will lead to excessive conflicts, and many of them are allocated with the same hash code, which leads to low performance efficiency.

• Other precautions
• Gethashcode rules: Gethashcode and Equals must adhere to specific rules. Equal objects must return the same hash code, and different objects may have the same hash code.
Hach code combination:

When considering the equal nature of multiple attributes, it is recommended to combine their hash code to reduce diagonal conflicts.

Convenient transportation: Considering providing the load == and! = The operator to facilitate comparison.

• By rewriting Gethashcode based on Equals, we ensure that objects with the same identification have the same hash code to promote efficient and accurate storage and retrieval in the collection.

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