On 21/08/2012 14:30, Simen Kjaeraas wrote:
On Tue, 21 Aug 2012 13:55:58 +0200, Regan Heath <[email protected]>
wrote:
I don't buy the argument that having to explicitly type ".get" will
stop anyone from automatically coding statements like:
val g: Option[T] = f.doSomething()
g.get.doSomethingElse()
So don't give them that access?
Yes, or force conversion of the Option, handling the invalid case:
g.valueOrElse(null).doSomethingElse();
The above being explicit that null might be returned. The code is no
safer, but it is much clearer. Also sometimes the caller has a better
alternative value than null to use which is actually valid.
I have an Option struct on my home computer that only allows access to
the held value if the error case is simultaneously handled:
Option!int a = foo();
int n = a.match!(
(int x) => x,
(None n) => 0 // or throw, or what have you.
);
The same solution is perfectly adaptable to MaybeNull, MaybeNan, and
probably
a host of others of the same family.
With some clever use of opDispatch, one could write an Option struct that
lets you call methods and acces members of the wrapped type, and return
Option!ReturnType.
Apart from the opDispatch bit, I've been slowly working on something
similar (Boost license):
https://github.com/ntrel/d-maybe/blob/master/maybe.d
I'm still working on it, but the basic ideas are there. I think the best
bit is apply(), which supports passing multiple Maybe values, calling
the delegate only if all Maybes are valid. In fact Maybe.map() is
unnecessary due to apply().
Nick
