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Editorial Team
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Asked: 2026-05-30T11:29:57+00:00

MSDN says : The default implementation of the GetHashCode method does not guarantee unique

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MSDN says:

“The default implementation of the GetHashCode method does not guarantee unique return values for different objects. “

But on the other hand, when I use the sn.exe tool it ensures a unique hash value to create a strongly-named assembly. If I did not get the point wrong, all the content of the assembly is converted to a hash value.

So, why GetHashCode()’s default implementation does not use the same algorithm used by sn.exe to create a unique hash values for objects and expects the developer to implent it?

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1 Answer

  1. Editorial Team

    Not enough bits. GetHashCode() returns 32 of them so there can never be more than 4 billion distinct values. The birthday paradox cuts that down considerably. The strong name generated by sn.exe (not sk.exe) uses a SHA1 hash. Which returns 160 bits, allowing for 2^160 distinct values.

    Which is a Really Big Number (1.4E48), ensuring uniqueness by the sheer quantity. Somewhat similar to a Guid which uses 128 bits. Not the same, a Guid generator ensures that no duplicates can occur, SHA1 has no such guarantee.

    GetHashCode has a limited number of bits because the primary requirement for the method is that it is fast. Short from providing the bucket index for hashed collections, its use is making equality testing fast. GetHashCode needs to be an order of magnitude faster than Equals(), give or take, to make it useful. That requires many corners to be cut, typically, the GetHashCode implementation for a struct that contains reference types for example only returns the GetHashCode value of the first member.

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