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Add note about exhaustive enum matching #46067

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Add note about exhaustive enum matching
ieviev May 9, 2025
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Update docs/fsharp/language-reference/enumerations.md
ieviev May 12, 2025
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4 changes: 4 additions & 0 deletions docs/fsharp/language-reference/enumerations.md
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Expand Up @@ -44,6 +44,10 @@ The default `enum` function works with type `int32`. Therefore, it cannot be use

Additionally, cases for enums are always emitted as `public`. This is so that they align with C# and the rest of the .NET platform.

To enable [exhaustive matching](match-expressions.md) for only the defined enum cases, you can suppress warning FS0104 using the directive `#nowarn "104"`. This allows the compiler to treat only declared enum values as valid during pattern matching, avoiding the need for a catch-all case — useful when you're certain all values are covered.

The warning FS0104 (`Enums may take values outside known cases.`) exists because enums can be assigned arbitrary underlying values, e.g. directly or as a result of [bitwise operations](https://learn.microsoft.com/dotnet/csharp/language-reference/builtin-types/enum#enumeration-types-as-bit-flags)

## See also

- [F# Language Reference](index.md)
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