I’m working my way through Hamish Anderson and Hanaan Rosenthal’s excellent Learn AppleScript. If you know a little about AppleScript but want to get a clearer understanding of what you’re doing and how to do it better, I highly recommend this book.
I believe I have found a flaw in one of the exercise scripts in the book, and I’ve spent a few days trying to figure out why it doesn’t work and how to fix it. I have failed.
At first I thought I had a typo somewhere in my script, but then I went to the book’s website and downloaded the code. The downloaded script gives me the same error as the one I had typed out myself.
It’s script 18-22 in the book. When I run it, I get this error:
Script Debugger highlights this line in the delete_associative_item handler:
set contents of record_ref to missing value
The script is below. What’s going wrong?
on make_associative_list()
(* Make a new associative list that stores values using any objects as keys.
Result: an associative list
Note: Users should not directly manipulate the contents of the returned
object. Instead, use the handlers provided to work with it safely.
*)
return {class:"associative list", the_items:{}}
end make_associative_list
on find_record_for_key(the_assoc_list, the_key)
(* This is a private handler. Users should not use it directly. *)
considering diacriticals, hyphens, punctuation and white space but ignoring case
repeat with record_ref in the_items of the_assoc_list
if the_key of record_ref = the_key then return record_ref
end repeat
end considering
return missing value -- The key wasn't found
end find_record_for_key
on get_associative_item(the_assoc_list, the_key)
(*
Get the value for the given key in an associative list.
the_assoc_list : associative list
the_key : anything -- the key to search for
Result : anything -- the value, if found
Note: Raises error -1728 if the key isn't found.
*)
set record_ref to find_record_for_key(the_assoc_list, the_key)
if record_ref = missing value then
error "The key wasn't found." number -1728 from the_key
end if
return the_value of record_ref
end get_associative_item
on set_associative_item(the_assoc_list, the_key, the_value)
(*
Set the value for the given key in an associative list.
the_assoc_list : associative list
the_key : anything -- the key to use
the_value : anything -- the new value
*)
set record_ref to find_record_for_key(the_assoc_list, the_key)
if record_ref = missing value then
set end of the_items of the_assoc_list to {the_key:the_key, the_value:the_value}
else
set the_value of record_ref to the_value
end if
return -- No return value; the handler modifies the existing associative list.
end set_associative_item
on count_associative_items(the_assoc_list)
(*
Return the number of items in an associative list.
the_assoc_list : associative list
Result : integer
*)
return count the_items of the_assoc_list
end count_associative_items
on delete_associative_item(the_assoc_list, the_key)
(*
Delete the value for the given key.
the_assoc_list : associative list
the_key : anything -- the key to delete
*)
set record_ref to find_record_for_key(the_assoc_list, the_key)
if record_ref is missing value then
error "The key wasn't found." number -1728 from the_key
end if
set contents of record_ref to missing value
set the_items of the_assoc_list to every record of the_items of the_assoc_list
return -- No return value; the handler modifies the existing associative list.
end delete_associative_item
set friends_ages to make_associative_list()
set_associative_item(friends_ages, "Bob", 35)
set_associative_item(friends_ages, "Jan", 38)
delete_associative_item(friends_ages, "Bob")
