Polar Studio

Error handling

On Error Statement

The On Error statement sets the behaviour for the current running procedure how to cope with errors. There are two flavours:

On Error Resume Next	Set the behaviour to ignore any errors. This will resume operation to the next statement, even if an error occured. The Err object can be used to see if something went wrong.
On Error Goto 0	This is the default behaviour. Will break on errors. If some error-handling is specified in a calling routine 'above' then the current routine will stop executing and the error will bubble-up.

Function OnErrorDemo
    Dim lErrorMessage As String
    
    On Error Resume Next
    
    DoSomeDatabaseUpdate 'Here, an error may or may not happen
    DoSomeOtherDatabaseUpdate 'Here, an error may or may not happen
    'Note: Each statement above will be executed
    
    If Err.Number <> 0 Then
        lErrorMessage = Err.Description 'This will contain the last Error message.
    End If
    
    Return lErrorMessage
End Function

Please notice the following:

The On Error statement can be useful if you want to perform a number of operations and it is not important if the fail or succeed
If possible try to avoid errors (even handled errors): Errors are notoriously slow and preventing them can speed up your application.

Try-Catch Statement

The Try-Catch statement is new in Polar Script. It will try to execute a number of lines. Once an error occurs, the rest of the lines is NOT executed (that is different from the On-Error-Resume-Next) and the execution will proceed to the Catch block or jump to the End Try. Using a Catch block is optional; within the Catch block, no error-handling is active anymore.

Note: In Polar Script, the 'Catch' block does not take any parameters. This is different from some other languages where the 'Catch' block can capture an exception object. In Polar Script, to access error details after catching an error, you should use the 'Err' object, as demonstrated in the Try-Catch examples.

Function TryCatchDemo
    Dim lErrorMessage As String
    
    Try
        DoSomeDatabaseUpdate 'Here, an error may or may not happen
        DoSomeOtherDatabaseUpdate 'Here, an error may or may not happen
        'Note: The second statement above will only be executed if the first succeeded
    Catch
        lErrorMessage = Err.Description
    End Try
    
    Return lErrorMessage
End Function

Error handling

On Error Statement

Try-Catch Statement

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