Discussion Thread: DIP 1040--Copying, Moving, and Forwarding--Community Review Round 1

[Walter Bright]

On 3/13/2021 11:47 AM, 12345swordy wrote:
> On Saturday, 13 March 2021 at 03:06:35 UTC, Walter Bright wrote:
>> On 3/11/2021 10:56 AM, 12345swordy wrote:
>>> How does it handle move constructors when a class have struct type variable 
>>> that is being alias this?
>>
>> #DIP1040 only applies to structs, not classes.
> 
> That doesn't answer the question.

The question doesn't make a lot of sense, as what does it have to do with classes?


> How does the DIP interact with the current alias this system?
> If I alias this a struct variable with move schematics in struct/class 
> definition called A, does A have the move schematics of the struct variable? 
> Replying "only applied to structs and not classes" isn't helpful here. I am not 
> talking about defining move schematics for classes, I am talking about the class 
> inheriting the struct that has move schematics defined, via alias this.

Classes don't inherit structs. But I will guess at what you mean.

We've discovered that alias this and classes produce a semantic quagmire that 
every proposed resolution just leads to worse weird cases. Hence:

1. I recommend NEVER using alias this in a class.

2. I'd like to make it illegal.

3. Any questions about how alias this works in a class, I refer to (1).

DIP1040 does not apply to classes. If you have a class that has an alias this 
that refers to a struct with move semantics, you're going to be sorry :-/

I recommend NEVER using alias this in a class.