Can you move a disabled this(this) struct in to a container type if it's an rvalue?

[Steven Schveighoffer]

On 12/13/18 8:17 AM, aliak wrote:
> On Thursday, 13 December 2018 at 12:08:22 UTC, Boris-Barboris wrote:
>> On Thursday, 13 December 2018 at 09:51:42 UTC, aliak wrote:
>>> [...]
>>
>>
>> You can just move in container constructor:
>>
>>
>> struct S {
>>     @disable this(this);
>>     this(int i) {}
>> }
>>
>> struct Container(T) {
>>     T value;
>>     this(T value) {
>>         import std.algorithm: move;
>>         this.value = value.move;
>>     }
>> }
>>
>> void main() {
>>     auto a = Container!S(S(3));
>> }
> 
> Ah. Is there any case where you would not want to do that when you have 
> a T value as parameter?

Probably not an issue. Note that if you take the parameter by value, the 
T must be an rvalue if it has disabled postblit.

In other words, this wouldn't work:

S s;
auto a = Container!S(s); // error

So moving it isn't going to affect anything outside the function.

> 
> And, what if it's "this()(auto ref T value)"? Then moving could be 
> dangerous if the parameter was passed as a ref. Or maybe it just 
> wouldn't compile?

What will happen is then you *could* take an already existing T as a 
parameter, and the T you pass in will be destroyed upon calling the 
constructor.

move resets the original to the .init value if it has a destructor or 
postblit.

Is it dangerous? Probably not, but you may want to document for anyone 
who uses the container to expect that.

-Steve