throw — Throws a user-defined exception or rethrows a caught exception.
throw( : : Exception : )
With the help of the operators try, catch, endtry, and throw it is possible to implement a dynamic exception handling in HDevelop, which is comparable to the exception handling in C++ and C#. The basic concepts of the exception handling in HDevelop are also described at the operators try, and dev_set_check as well as in the “HDevelop User's Guide”.
The operator throw provides an opportunity to throw an exception from an arbitrary place in the program. This exception can be caught by the catch operator of a surrounding try-catch block. By this means the developer is able to define his own specific error or exception states, for which the normal program execution is aborted in order to continue with a specific cross-procedure exception handling, e.g., for freeing ressources or restarting from a defined state.
In such a user-defined exception a nearly arbitrary tuple can be thrown as the Exception parameter, merely the first element of the tuple should be set to a user-defined error code >= 30000.
In addition, with the help of the operator throw it is possible to rethrow an exception that was caught with the operator catch. This may be sensible, for instance, if within an inner try-catch-endtry block (e.g., within an external procedure) only specific exceptions can be handled in an adequate way and all other exceptions must be passed to the caller, where they can be caught and handled by an outer try-catch-endtry block.
For rethrowing a caught exception, it is possible to pass the Exception tuple that was caught by the catch operator directly to the Exception parameter of the throw operator. Furthermore, it is possible to append arbitrary (but no iconic) user data to the Exception tuple, that can be accessed after catching the exception as 'user_data' with the operator dev_get_exception_data:
try ... catch (Exception) ... UserData := ... throw ([Exception, UserData]) endtry
The export of the operators try, catch, endtry, and throw is not supported for the languages C and VisualBasic 6.0, but only for the languages C++, C# and VisualBasic/.NET. Only the latter support throwing exceptions across procedures.
Tuple returning the exception data or user defined error codes.
If the values of the specified parameters are correct throw (as operator) returns 2 (H_MSG_TRUE). Otherwise an exception is raised and an error code returned.