On Fri, 04 Sep 2009 22:45:40 -0400, Rainer Deyke <[email protected]>
wrote:
Steven Schveighoffer wrote:
I disagree, how many ways do you want to say something is unset? I
think one case -- is this thing null -- is plenty for 99% of cases.
Your case, well, I had trouble understanding it, but I think the nuance
of how something is unset is not usually important.
Possible use case for Optional: storing an upper limit. In this case
"null" means "there is no upper limit".
Possible use case for Optional: a function that retrieves a value from a
configuration file. In this case, "null" means "the value is not found
in the configuration file".
So what happens if you want to store that there is no upper limit in a
configuration file?
Why do you care if it was or was not found in the configuration file
beyond the call to retrieve it? Pass in a default value (of null if you
wish), or have the function return a separate boolean indicating whether
it was found or not. Using a new type just to determine if something was
found during a function call seems like a waste to me. If there's a
reason to store that fact beyond the function call, then create a new type
which stores that fact. You shouldn't complicate the syntax for the sake
of a corner case.
What do you think is more confusing?
auto val = getConfig("upperlimit")
if(val is null)
upperLimit = default_upper_limit;
else
upperLimit = *val;
- or -
upperLimit = getConfig("upperlimit", default_upper_limit);
I think that what you will find with a solution that *does* allow this,
you will be sacrificing something else -- such as syntax clarity or a
member function.
No, keeping the container and the containee separate leads to /clearer/
(if slightly more verbose) syntax. My proposal is to use use pointer
syntax:
Optional!T v;
f(v); // Do something with the container.
f(*v); // Do something with the containee.
Hm... that means you have to use *v every time you want the value, and
just v if you want to check for null? I think the most common case is
using the containee, I'd rather have that be the default.
-Steve
