Defer in ActionScript

ActionScript doesn’t have a direct equivalent to Go’s defer keyword. However, we can simulate similar behavior using try/finally blocks. Here’s how we could implement a similar concept in ActionScript:

package {
    import flash.filesystem.File;
    import flash.filesystem.FileMode;
    import flash.filesystem.FileStream;
    import flash.system.System;

    public class DeferExample {
        public function DeferExample() {
            main();
        }

        private function main():void {
            var f:FileStream = createFile("/tmp/defer.txt");
            try {
                writeFile(f);
            } finally {
                closeFile(f);
            }
        }

        private function createFile(p:String):FileStream {
            trace("creating");
            var file:File = new File(p);
            var stream:FileStream = new FileStream();
            try {
                stream.open(file, FileMode.WRITE);
                return stream;
            } catch (error:Error) {
                throw new Error("Failed to create file: " + error.message);
            }
        }

        private function writeFile(f:FileStream):void {
            trace("writing");
            f.writeUTFBytes("data\n");
        }

        private function closeFile(f:FileStream):void {
            trace("closing");
            try {
                f.close();
            } catch (error:Error) {
                trace("Error: " + error.message);
                System.exit(1);
            }
        }
    }
}

In this ActionScript example, we’re using a try/finally block to ensure that the file is closed after we’re done writing to it, regardless of whether an exception occurs or not. This mimics the behavior of Go’s defer statement.

Here’s a breakdown of the changes:

1. We’ve replaced Go’s package system with ActionScript’s package structure.
2. Instead of using Go’s os package, we’re using ActionScript’s flash.filesystem classes for file operations.
3. The panic function is replaced with throwing an Error.
4. fmt.Println is replaced with ActionScript’s trace function for console output.
5. Error handling is done using try/catch blocks instead of checking returned error values.
6. The main function is replaced with a constructor function, which is typical in ActionScript.

To run this program in a Flash environment:

$ mxmlc DeferExample.as
$ adl DeferExample-app.xml
creating
writing
closing

Note that ActionScript runs in a sandboxed environment, so file operations might be restricted depending on your security settings. You may need to adjust the paths or permissions accordingly.

This example demonstrates how to implement a deferred execution pattern in ActionScript, ensuring that cleanup operations are performed even if an error occurs during the main execution.