In Python I use 'with psycopg2.connect() as conn:' for database connections. How do I manage resources in EK9?

EK9 uses try-with-resource for automatic cleanup, similar to Python's 'with' statement.

Python:

  with psycopg2.connect(connString) as conn:
      cursor = conn.cursor()
      cursor.execute('SELECT ...')
      results = cursor.fetchall()
  # conn automatically closed here

EK9:

  try
    -> connection <- openConnection(connString)
    results <- queryDatabase(connection, sqlQuery)
    processResults(results)
  catch
    -> ex as Exception
    stderr.println(`Database error: ${$ex}`)
  finally
    cleanup()

The try -> resource <- expr() pattern declares a resource that is automatically closed when the try block ends. The -> means 'data flowing in' — the connection is the resource being managed.

If the resource implements close(), EK9 calls it automatically — like Python's __exit__() or Java's AutoCloseable.

Example

defines module qa.gettingstarted.frompythonconnection

  defines function

    buildGreeting() as pure
      -> personName as String
      <- rtn as String: "Hello, " + personName

  defines program

    ConnectionPatternDemo()
      stdout <- Stdout()
      stderr <- Stderr()

      // Pattern: try-with-resource for connection-like objects
      // In Python: with open('file.txt') as f: data = f.read()
      // In EK9: try -> resource <- openResource() ... catch/finally

      try
        greeting <- buildGreeting("Database User")
        stdout.println(greeting)
      catch
        -> ex as Exception
        stderr.println(`Error: ${ex}`)
      finally
        stdout.println("Cleanup complete")

Common mistakes

E01073 — 'null' does not exist in EK9. Use try-with-resource for connections: 'try -> connection <- expr()'. See ek9 -h E01073.

Incorrect:

      connection <- openConnection(connString)
      if connection != null
        processData(connection)

Correct:

      try
        greeting <- buildGreeting("Database User")
        stdout.println(greeting)

Other ways to ask this

What is the EK9 equivalent of Python's context manager for connections?
How do I safely open and close a connection in EK9?
How does EK9 handle resource cleanup like Python's with statement?

Coming from another language?

Python developers: your 'with X as y:' pattern becomes EK9's 'try -> y <- X'. The finally block replaces __exit__. Exception handling uses catch -> ex as Exception.

Keywords: resource, with, connection, python, migration, cleanup, try