byref parameters starting with some non-ASCII identifiers cannot be set.

[ijklam]

byref parameters whose identifier starting with some non-ASCII (like Chinese characters) cannot be set.

Repro steps

Enter this code in fsi:

let f (x: int byref) = x <- x + 1
let f3 (a叉: int byref) = a叉 <- a叉 + 1
let f2 (叉: int byref) = 叉 <- 叉 + 1 // fails to compile
let f4 (叉a: int byref) = 叉a <- 叉a + 1 // fails to compile

Expected behavior

The code can be compiled successfully

Actual behavior

A FS0027 was thrown.

Known workarounds

Don't use non-ASCII identifiers.

Related information

Provide any related information (optional):

• Windows 11 23H2
• .NET 9 with F#9
• Editing Tools: fsi or ionide-vscode

[ijklam]

Update: Even the capital-letter-leading byref parameters are considered as immutable. Is this by designed?

It seems that this is because these functions are firstly be parsed to a lambda with a match rather than a normal lambda.

let f2 (叉: int byref) = 叉 <- 1;;

let f2 (a: int byref) = a <- 1;;

[brianrourkeboll]

That seems pretty unlikely to me to be by design.