Exceptions: The invalidArg Function
The invalidArg
function generates an argument exception.
invalidArg parameter-name error-message-string
The parameter-name in the previous syntax is a string with the name of the parameter whose argument was invalid. The error-message-string is a literal string or a value of type string
. It becomes the Message
property of the exception object.
The exception generated by invalidArg
is a System.ArgumentException
exception. The following code illustrates the use of invalidArg
to throw an exception.
let months = [| "January"; "February"; "March"; "April";
"May"; "June"; "July"; "August"; "September";
"October"; "November"; "December" |]
let lookupMonth month =
if (month > 12 || month < 1)
then invalidArg (nameof month) (sprintf "Value passed in was %d." month)
months[month - 1]
printfn "%s" (lookupMonth 12)
printfn "%s" (lookupMonth 1)
printfn "%s" (lookupMonth 13)
The output is the following, followed by a stack trace (not shown).
December
January
System.ArgumentException: Value passed in was 13. (Parameter 'month')
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