On Sat, 31 Mar 2012 01:46:19 +1100, Andrei Alexandrescu
<seewebsiteforem...@erdani.org> wrote:
Starting a new thread from one in announce:
http://prowiki.org/wiki4d/wiki.cgi?LanguageDevel/DIPs/DIP16
Please comment ...
We solved this issue in the Euphoria Programming language by introducing
the concept of 'public include'.
The 'include' directive is similar to DPL's 'import' directive. Normally
when a file (module) is included, its public identifiers are *only*
visible to the including module and not further module up the include
tree. However, if a module is 'public include'd then its public
identifiers are set up *as if* they were actually declared in the
including module rather than the included module.
Thus if Euphoria's module called datetime.e gets too large, we split it
into, say two or three new modules and replace the code in datetime.e with
corresponding 'public include' statements, thus making it a type of
package definition. This means that existing application code does not
have to be modified and future code can choose to include either the
entire package called datetime.e or individual modules that go into making
that package.
From the POV of a developer, creating a package out of what was a module
is transparent. They do not even know or have to care in order to use it.
There are no complicated access rules that can one day trip people up.
We made one tweak to the public identifier declaration though to cater for
situations in which an identifier which was currently local to a module,
but when moved to a new module when the original was transformed to a
package, still had to be visible to the code in the package file but
invisible to code including the package. We created the 'export' qualifier
on an identifier declaration to signal such an item.
Original module code ...
function to_seconds(datetime x) /* A local function to the module */
public function local_to_gmt(datetime x) /* A publicly exposed function
*/
New module code ...
export function to_seconds(datetime x) /* A function visible to the
package file only */
public function local_to_gmt(datetime x) /* A publicly exposed function
*/
This means that application that include the package datetime.e will not
see to_seconds() but code in the datetime.e will see it, and
local_to_gmt() will be seen by the application code and the package code.
--
Derek Parnell
Melbourne, Australia
