Error handling

Exceptions

A Try/Catch block is an error-handling construct that allows custom code to be executed in situations which may otherwise cause undesirable behaviour.

The Try/Catch block opens with Try and closes with End (or End Try). The code to be executed within must be followed by at least one Catch section.

In the event of an error occurring within the Try/Catch block, an exception object (based on the native Throwable class) should be 'thrown' via the Throw instruction.

If an exception occurs, program flow jumps to a Catch section declared explicitly for the given exception type. The exception object is 'caught' and the relevant error-handling code is executed.

You can declare multiple exception classes to handle different types of exception and should create a matching Catch section for each one.

After an exception is caught and handled, program flow exits the Try/Catch block and continues.

When a Try block has multiple Catch blocks and an exception is thrown, the first Catch block capable of handling the exception is executed. If no suitable Catch block can be found, the exception is passed to the next most recently executed Try block, and so on.

If no Catch block can be found to catch an exception, a runtime error occurs and the application is terminated.

The Try/Catch method of error-handling allows code to be written without the need to manually check for errors at each step, provided an exception has been set up to handle any errors that are likely to be encountered.

Syntax:

Try

    ...code (sould contain at least one 'throw')...

Catch exception

    ...error handling code...

End

Example code:

#Import "<std>"

Using std..

Class CustomException Extends Throwable
    Field msg:String

    Method New (message:String)
        Self.msg = message
    End
End

Function Main:Void()
    Local somethingWrong := True

    Try

        If somethingWrong Then Throw New CustomException ("Custom Exception detected")

    Catch err:CustomException

        Print err.msg

    End
End