On Tuesday, 8 August 2017 at 18:57:48 UTC, Steven Schveighoffer
wrote:
On 8/8/17 2:34 PM, Johan Engelen wrote:
Hi all,
How would you express the function interface intent that a
reference to a class may not be null?
For a function "void foo(Klass)", calling "foo(null)" is
valid. How do I express that that is invalid? (let's leave
erroring with a compile error aside for now)
There isn't a way to do this in the type itself.
One can always create a null class instance via:
MyObj obj;
There is no way to disallow this somehow in the definition of
MyObj. With structs, you can @disable this(), and it's still
possible but harder to do so.
Ok thanks, so this could be a reason for not being allowed to
express the non-null-ness.
(I still haven't found peace with the absence of an explicit *
for classes)
I would say, however, that if you wanted to express the
*intent*, even without a compile-time error, you could use a
contract:
void foo(Klass k) in {assert(k !is null);};
Thanks. I regret leaving compile-time errors out, because in that
case adding it to the function documentation would suffice.
(Btw: "Error: function foo in and out contracts require function
body". But who uses .di files anyway. ;-)
Cheers,
Johan
