Greetings

Kindly take a look at the code below. I am using alias this with a function that returns by value. I believe in such cases the alias should not take affect when an instance of foo is being used as an lvalue. As a result elements of bar should not have been visible inside the constructor of foo.

Please comment. Is this a bug?

Regards
- Puneet

struct bar (bool B, N...) {
  int n = 0;
}

struct foo (N...) {
  bar!(true, N) _bar = void;

  bar!(true, N) getN() {
    return _bar;
  }

  alias getN this;

  public this(T) (T other)
    if (is(T unused : int)) {
    n = other;
  }
}


void main() {
  import std.stdio;
  foo!8 a = 42;
  writeln(a.n);
}

Hi,

I tested the code you provided and extended it a little and here is the result:

struct bar (bool B, N...) {
 int n = 0;
}

struct foo (N...) {
 bar!(true, N) _bar = void;

 bar!(true, N) getN() {
   return _bar;
 }

 alias getN this;

 public this(T) (T other)
   if (is(T unused : int)) {
   n = other;
 }
}

void aFunc( bar!( true, 8 ) zeBar ) {
  //Subtyping compiles.
}

bar!( true, 8 ) aSecondFunc() {
  return bar!( true, 8 )();
}

struct toto{
  size_t payload;
}

toto aThirdFunc() {
  return toto();
}

void main() {
 import std.stdio;
 foo!8 a = 42;
 writeln(a.n); //Prints 0, as it should.
 aFunc( a ); //The alias this correctly allows for subtyping, as advertised
 a.getN().n = 3; //Allowing for rvalue manipulation is indeed weird, but apparently in a coherent fashion, not just for the alias this case.
 writeln(a.n); //Still prints 0, as it should.
 aSecondFunc().n = 4;
 aThirdFunc().payload = 10; //Without alias this, without templates, juste plain rvalue. Another coherent example, yet questionably permitted.
}

Therefore, your question, I believe, is more related to rvalues directly rather than alias this, if I get your meaning right. The question is still very relevant and I was surprised to find out about the current behaviors of rvalues.