why @property cannot be pass as ref ?

[ChangLong]

On Wednesday, 3 January 2018 at 08:51:55 UTC, Simen Kjærås wrote:
> On Saturday, 30 December 2017 at 03:49:37 UTC, ChangLong wrote:
>> What I am try to do is implement a unique data type. (the 
>> ownership auto moved into new handle)
>
> Have you considered std.typecons.Unique[0]? If yes, in what 
> ways does it not cover your needs?
>
> Your example code written with Unique would be something like 
> the below, with some additions to show off more of what it can 
> do:
>
> import std.typecons : Unique;
> import std.algorithm.mutation : move;
>
> void test1(size_t i) {}
> void test2(ref size_t i) {}
> void test3(ref Unique!size_t i) {}
> void test4(Unique!size_t i) {}
>
> unittest
> {
>     static __gshared size_t socket;
>     auto l1 = Unique!(size_t)(&socket);
>     assert(l1 == &socket);
>
>     Unique!(size_t) l2 = void;
>     assert(!is(typeof({
>         l2 = l1; // Fails to compile - cannot copy Unique.
>     })));
>     move(l1, l2); // Explicit move using 
> std.algorithm.mutation.move.
>
>     assert(l1 == null); // l1 has been cleared - only one 
> reference to the data exists.
>     assert(l2 == &socket); // l2 has the only reference.
>
>     auto l3 = l2.release; // Implicit move, not unlike your 
> byRef call.
>
>     assert(l2 == null); // l2 has been cleared - only one 
> reference to the data exists.
>     assert(l3 == &socket); // l3 has the only reference.
>
>     assert(!is(typeof({
>         auto l4 = l3; // Fails to compile - cannot copy Unique.
>     })));
>
>     test1(*l3); // Can dereference and pass the pointed-to 
> value.
>     test2(*l3); // Can pass reference to pointed-to value[1].
>     test3(l3);  // Lets you pass references to Unique.
>     assert(!is(typeof({
>         test4(l3); // Fails to compile - cannot copy Unique.
>     })));
> }
>
> [0]: https://dlang.org/library/std/typecons/unique.html
> [1]: This surprised me a little - that's a new reference to the 
> pointed-to value, which the callee could squirrel away 
> somewhere it shouldn't. I guess it's there for ease of use.
>
> --
>   Simen

Thanks for explain. I need add version number and other check 
into the UniqueType,  std.typecons : Unique is is not suit.

std.algorithm.mutation : move is what I am look for.  but I don't 
understand why this code not working since I already add void 
opAssign(ref This ) to UniqueType.

  Unique!(size_t) l1 =  Unique!(size_t)(&socket);
  Unique!(size_t) l2 = void;
  l2 = l1;  // assign left value into left value,  Unique is not 
copyable because it is annotated with @disable