Escape this in pure members

[DlangUser38]

On Tuesday, 22 September 2020 at 18:21:10 UTC, Jacob Carlborg 
wrote:
> On 2020-09-19 21:50, Per Nordlöw wrote:
>> On Saturday, 19 September 2020 at 18:48:31 UTC, Jacob Carlborg 
>> wrote:
>>> A nested class seems to be able to escape the `this` 
>>> reference:
>> 
>> Ahh, thanks.
>> 
>> I just realized that it can escape into other parameters 
>> without the `scope` qualifier?
>> 
>> This
>> 
>> class Bar
>> {
>>      void bar(scope Bar b) @safe pure
>>      {
>>          b = this;
>>      }
>> }
>> 
>> compiles but this
>> 
>> class Bar
>> {
>>      scope void bar(scope Bar b) @safe pure
>>      {
>>          b = this; // Error: scope variable `this` assigned to 
>> `b` with longer lifetime
>>      }
>> }
>
> Hmm, why would `b` have longer lifetime? Isn't the lifetime of 
> `b` throughout `bar`?

The following analysis might be wrong but I think that `scope` as 
a **member** function attribute is not supposed to be used as 
that is not even documented.

So it would works "by default". The compiler thinks that `this` 
is a scope variable that will stop living after `bar()`.

Also as `b` is not `ref` this is clearly a wrong diagnostic. 
There's a special case missing in the compiler.