On 6/18/18 2:58 PM, aliak wrote:
On Monday, 18 June 2018 at 17:58:11 UTC, Steven Schveighoffer wrote:
What then can happen is that your local calls can get hijacked from
outside the module, if someone happens to define something later that
you happened to import. D tries to avoid such possibilities.
There's not much precedent for local symbols being overridden by
module-level symbols.
I thought that happens already with non-nested functions:
module a;
struct A {
void f(); // assume it's added later
}
module b;
import a;
void f(A) { }
void g() {
auto x = A();
a.f(); // this would be calling local f until someone added A.f
}
Or I misunderstood what you said?
It's the same in the fact that your call is silently switched to a
different call. However, in the current syntax, an external entity
CANNOT override a local function. When you call the nested function,
it's the nested function, no matter what else occurs outside (even in
the local module). There is no precedent for local functions to be
overridden by module-level functions.
So if we allow this, we break a guarantee of which function is called,
albeit via a different syntax. Generally, the local function takes
precedence, then the member functions, then module-level functions.
Making the module level functions override the local functions is not
normal or expected. Generally you are defining locals to override what
you see outside the function.
But with UFCS, it's treated as part of the API of the type. The type
defines the API first, and then you can add to it, you can't override it.
Part of this is historical in nature -- UFCS came after member
functions, and so they had to be lower priority.
PS: This is something I've worried about before actually [1] when I was
more of a noob than now, but I've come to accept I guess :) .... though
I could still be misunderstanding things of course :/
https://forum.dlang.org/post/crcbaautgmrglhzvx...@forum.dlang.org
I think the current state of affairs still leaves some hijacking doors
open, depending on your point of view. It's certainly not perfect. The
only way to be sure you are doing things correctly is to use member
syntax when you know it's a member, and function syntax otherwise.
IMO, UFCS for locals isn't going to change, but I could also be wrong.
It's not really up to me what goes into the language, I just am trying
to help explain the rationale behind the current rules.
-Steve
