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Why does an enum support 251 values (and not 256)?

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Posted on by JB-22101400-0

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From X++ docs at https://learn.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/dev-ref/xpp-data-primitive#enum -

"[Y]ou can declare up to 251 (0 to 250) literals in a single enum type"

This restriction seems rather odd to me. Why 251, specifically? Given how close it is in value to 256, it seems logical to conclude that enums are stored under the hood as bytes - but if so, why not let us use all 256 possible values?

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André Arnaud de Cal... 303,383 Super User 2026 Season 1 on at

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Hi JB,

This is a design decision that comes from Dynamics AX version 1.0. It has never been changed anymore. Do you really need 256 enumerations?

In the SQL database, it is not a byte, at least not anymore. It is stored as BigInt. In the past, I did a test and was able to write and read data with X++ coding using a value of 1000 and higher. I was bypassing the enumeration data type for this test.

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