Daniel Keep wrote:
Andrei Alexandrescu wrote:
I plan to add a Nullable struct to Phobos (akin to C#'s Nullable,
Boost's Optional).
Apparently a good design is to define Optional!T with a minimum of
member functions (ideally none) and have it use the "alias this" feature
to masquerade as a T. That way Optional!T looks and feels much like a T,
except that it supports a function
bool isNull(T)(Optional!T value);
Am I on the right track? If so, what is the name you'd prefer for this
artifact?
Andrei
Given the apocalyptic battle raging in this thread at the moment, maybe
it would be pertinent to have both. Sometimes, you do want a generic
mechanism for representing "this may or may not have a value". Other
times, you just want something with a "no value set" sentinel.
Nullable!T would be a type for which 'null' is a valid value. By this
definition, Nullable!(Nullable!T) is obviously equivalent to Nullable!T;
it's equivalent to T if T is either a pointer, array or object.
Optional!T would be a type where an instance may or may not have a value
of type T; even if T is itself Optional.
I'm tempted to put an alias this into Optional and just define an
external contentsOf function that pulls out the value contained in the
Optional. Not sure if that's the right choice or not.
So that gives us:
[snip]
Thanks. I think what I'll do for now is define Optional and see where
things go.
Andrei
