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

[Walter Bright]

On 3/17/2021 11:14 PM, Elronnd wrote:
>> If a Move Constructor is not defined for a struct that has a Move Assignment 
>> Operator, a default Move Constructor is defined and implemented as a move for 
>> each of its fields, in lexical order.
> 
> I think the order should be undefined.  Forcing the moves to happen in lexical 
> order may inhibit some optimizations; and code which relies on the order of 
> implicit moves is fragile anyway and shouldn't be encouraged.  If the order is 
> important for legitimate reasons, then those reasons should be made explicit in 
> the code with an explicit move constructor.

The trouble with that is the user may inadvertently rely on the 
implementation-defined order, and his code will break when using another 
implementation.

The optimization advantage, if any, would be slight and not worth the risk.