• Timothee Cour (15/15) May 17 2013 How to have alias this with an unaccessible member (x below).
• Dicebot (12/12) May 18 2013 Will this do?
• Dicebot (11/11) May 18 2013 Btw, fun fact. This code crashes 2.063 beta:
• Timothee Cour (28/40) May 23 2013 This won't do for the same reason: now 'get' is made public so we're bac...

Timothee Cour <thelastmammoth gmail.com> writes:

How to have alias this with an unaccessible member (x below).
Making the member private won't work as it'll disable all operations on
said member.

----
struct A(T){
  T x;
  //private T x would prevent alias this from doing anything useful
  alias x this;
}
void main(){
  auto a=A!int;
  a++;//should do a.x++;
  static assert(!__traits(compiles,a.x)); // I want this to hold

}
----

"Dicebot" <m.strashun gmail.com> writes:

Will this do?

--------------------

struct A(T)
{
     private T x;

     ref T get()
     {
         return x;
     }

     alias get this;
}

---------------------

"Dicebot" <m.strashun gmail.com> writes:

Btw, fun fact. This code crashes 2.063 beta:

------------------------

struct A(T)
{
     private T x;
     alias y = x;
     alias y this;
}

------------------------

dmd: aliasthis.c:114: virtual void AliasThis::semantic(Scope*): 
Assertion `t' failed.

Timothee Cour <thelastmammoth gmail.com> writes:

This won't do for the same reason: now 'get' is made public so we're back
to the same problem (inverting roles of x and get).

However what about changing the behavior of alias this as follows:

when a member/method x is private, "alias x this" behaves as if x was not
declared private.

I think this makes sense:
* this allows protection (x is an implementation detail) so that 'this'
behaves exactly as 'x'
* also, without this change of behavior, "alias x this" would not make any
sense in terms of behavior outside the class (inside behavior should just
access x directly)

Then, when multiple alias this statements will become allowed in D, we
would have implemented the same concept as "embedding" in GO.

Any thoughts?


here's what we would have:
----
struct A(T){
  private T x would prevent alias this from doing anything useful
  alias x this;
}
void main(){
  auto a=A!int;
  a++;//should do a.x++; //semantic change: even though x is private, all
its methods are un-privated through alias this.
  static assert(!__traits(compiles,a.x));
}
----




On Sat, May 18, 2013 at 1:33 AM, Dicebot <m.strashun gmail.com> wrote:

 Will this do?

 --------------------


 struct A(T)
 {
     private T x;

     ref T get()

     {
         return x;
     }

     alias get this;
 }

 ---------------------