throw

Typecontrol structure
DictionaryLCS
LibraryLiveCode Script
Syntax
throw <errorString>
Summary

Returns an error message to a control structure.

Introduced1.0
OSmac, windows, linux, ios, android
Platformsdesktop, server, mobile
Parameters
NameTypeDescription
errorString

The string that is returned to the calling try control structure. The errorString becomes the parameter of the catch line in the try control structure.

Example
open file tFile for text read
if the result is not empty then
  throw "failed_to_open_file"
end if
RelatedKeyword: string, catch
Message: errorDialog
Function: commandNames
Glossary: return, call, handler, execute, statement, message, negative, control structure, parameter, command, object
Control Structure: return, try
Description

Use the throw control structure in a handler called from within a try control structure.

Form: The throw statement appears on a line by itself, anywhere inside a handler.

If LiveCode generates the error (for example, an execution error from a built-in command), it returns a positive number to the try control structure. To avoid confusion, therefore, a throw control structure should return a negative number, or a non-numeric string.

If a throw control structure is executed in a handler that was not called from within a try control structure, an errorDialog message is sent to the object, and the errorString is passed as a parameter.

Note: The throw control structure is implemented internally as a command and appears in the commandNames.