Re: [boost] [variant] Please vote for behavior (Was: Basic rvalueand C++11 features seupport)

Subject: Re: [boost] [variant] Please vote for behavior (Was: Basic rvalueand C++11 features seupport)
From: Peter Dimov (lists_at_[hidden])
Date: 2013-01-21 12:47:43

Louis Dionne wrote:
> My vote goes to II.
>
>     - Using moved-from objects should rarely happen, if ever.
>     - It is not even a breaking change since move from variants was not
>       supported in the past.

That's not quite true. If a type doesn't have a move constructor, move is 
supported and same as copy.

> Moreover, I am explicitly against proposition III:
>
>     - The state of the moved-from variant is not explicitly set by the
>       programmer. I tend to prefer explicit to implicit.
>     - The type held in the moved-from variant depends on the types in the
>       variant, which could make it harder to use variants in generic code.

I fail to grasp the logic that simultaneously holds that

>     - Using moved-from objects should rarely happen, if ever.

and then proceeds to argue that moved-from objects should not be left in 
such-and-such valid state, but must be left in an invalid state instead.