On Wednesday, 5 February 2014 at 00:47:27 UTC, Walter Bright
wrote:
The difficulty comes when needing to transfer the nullability
of the argument to the nullability of the return type. Implicit
conversions don't help with that.
See inout.
You could always do it with a template; T identity(T t) { return
t;} will literally work. (I'm pretty sure it would also work with
const and immutable; the reason inout exists isn't that it is
impossible, it is just to counter template bloat)
Is this common enough to warrant an addition, or would templates
be good enough when it is needed? inout has a very common real
world use case: slicing.
inout(char)* strchr(inout(char)* haystack, in char* needle);
What's the real world equivalent to strchr with regard to
nullability?
* typeof(this) inside a class is never nullable. You can't call a
method with a null this. So a method that returns this can always
just return the regular (not null) type.
* this[x..y] is never nullable. Slicing a null reference is
illegal, so again, no need to offer the nullable overload.
* Returning a field of a nullable type is illegal, dereferencing
null to get to the fields is illegal. Whereas a struct might
return inout(member_variable), it never makes sense to do
inout_nullability(member_variable).
I can't think of a single real world case where you'd need
this... and if I'm wrong, we can always use a template and/or
revisit the problem later.
