How do I use `__rvalue` expression on a struct property?

[Timon Gehr]

On 4/24/25 10:23, Jiten Devlani wrote:
> I'm exploring the new `__rvalue` expressions, and got stuck while 
> creating a move constructor for a container(non-copyable) with a non- 
> copyable container property.
> 
> ```d
> import core.stdc.stdio : printf;
> import core.memory : pureMalloc, pureFree;
> struct S {
>      @("mallocd") ubyte[] p;
>      this() @disable;
>      this(this) @disable;
>      this(ubyte[] p) @nogc @trusted nothrow {
>          printf("Base constructor!\n");
>          this.p = p;
>      }
> 
>      this(S rhs) @nogc @trusted nothrow {
>          printf("Move constructor!\n");
>          p = rhs.p;
>          rhs.p = null;
>      }
> 
>      ~this() pure @nogc @trusted nothrow {
>          if (p) {
>              pureFree(p.ptr);
>              p = null;
>          }
>      }
> }
> 
> struct Container {
>      S s;
>      this() @disable;
>      this(this) @disable;
>      this(S s) @nogc @trusted nothrow {
>          this.s = __rvalue(s);
>      }
> 
>      this(Container rhs) @nogc @trusted nothrow {
>          this.s = __rvalue(rhs.s);
>      }
> }
> ```
> 
> Above code results in compilation error:
> ```
> <source>(35): Error: struct `example.S` is not copyable because it has a 
> disabled postblit
>          this.s = __rvalue(rhs.s);
> ```
> 
> I've looked into the language reference but could not find a way to move 
> a property of a rvalue object instance.

Seems this is a bug, you can report it here:
https://github.com/dlang/dmd/issues/new

This workaround appears to work:

```d
     this(Container rhs) @nogc @trusted nothrow {
	    scope tmp=&rhs.s;
	    this.s = __rvalue(*tmp);
     }
```