OpenEuphoria

Re: object(x) rethink

• Posted by Robert Craig <rds at RapidEup??ria.com> Mar 04, 2008
• 730 views

All types in Euphoria, whether they are
built-in, like integer(), or user_defined,
can be used to either declare a variable,
or test if a value belongs to that type.
e.g.

atom a
    sequence s
    my_special_type month

    if atom(9.9) then ...
    if sequence(x) then ...
    if my_special_type(11) then ...

So, just for completeness, if you can
declare something as:
    object y
it seems reasonable that you should
be able to say:
    if object(z) then ...
even if that is rather pointless.

As for detecting uninitialized variables,
this would be trivial to implement in the
interpreter as it is currently implemented.

It would be harder to implement in the translator,
since the translator currently does no run-time 
checking at all for uninitialized variables.
You would have to initialize variables to the
magic "NOVALUE", something that is currently not done.
This might waste a bit of time, in the case of
private variables that would have to be set to NOVALUE
each time a routine was called. (In some cases I 
currently set certain variables to 0 to achieve 
an optimization later on.)

All future implementations of Euphoria,
interpreted, compiled, etc. would
have to support this, even if it proved to
be inconvenient for the implementor.

Currently Euphoria can often detect *at compile-time*
that a variable is never assigned a value.

I'd like to see some good examples of where
this would be useful. It seems to me you
could have code that detected that a variable
was not initialized, but then what would you
typically do? Probably either issue an error
message "Variable not initialized!", or quietly
set the variable to some default value.

If the program was composed entirely of your own
code, it would be silly to add *error-checking* code 
to test if a particular variable is initialized. 
It would be easier just to initialize it.
If you wanted to test that it "hasn't really
been set to a meaningful value yet", e.g. a file handle,
in almost all cases you can just set it to some special 
value that indicates that fact, like -1, or whatever.

If you wrote a library used by others, they might
fail to initialize one of your global variables, maybe because they
made a silly mistake, or just didn't realize it was
required. So in that case you could either issue an error message
telling them they made a mistake, or quietly set the 
variable to some default value. Your message might be
slightly more meaningful to them, than a generic
Euphoria-issued message, but probably not much.
You could also initialize the variable yourself to some
special value that means "not really initialized properly yet"
and issue the same kind of message.

I don't think this is a good idea,
but I would not oppose it if a majority
wanted it, and someone were willing to
implement it.

Regards,
   Rob Craig
   Rapid Deployment Software
   http://www.RapidEuphoria.com