Beta D 2.068.1-b2

[Steven Schveighoffer via Digitalmars-d-announce]

On 9/4/15 8:14 AM, Steven Schveighoffer wrote:

> Why did this compile/pass tests then? I wasn't aware of this restriction.
>
> https://github.com/D-Programming-Language/phobos/pull/3572

OK, I dug into it further.

It seems that under some level of detection of whether a function that 
could be called on the base is really called on the derived, then the 
derived function is not allowed to mask the base function.

HOWEVER, if the call would result in an error instead, then the override 
is totally fine, and calling the function on a base reference actually 
calls the masked function. This seems incorrect, when you mask a 
function, I would consider that to be hidden also.

So technically, the error is that the toString masking could be called 
in the same way the base could be called (given the default parameter).

This sure seems arbitrary to me. I remember the whole thing about 
function hijacking, but this hidden function "feature" doesn't make a 
lot of sense. In one case, you can hide it, but still access it from the 
base, in another, the compiler was rewriting the vtable to not allow you 
to access it from the base, on what seems to be an arbitrary concern. 
And that now is a compiler error.

I wonder how this will affect multiple alias this, since you could 
potentially have a type that converts to two disjoint types, but 
wouldn't be known to the compiler if a base and derived class accepted 
the disjoint types.

-Steve