DIP 1016--ref T accepts r-values--Formal Assessment

Steven Schveighoffer schveiguy at gmail.com
Thu Jan 31 15:09:17 UTC 2019

On 1/31/19 3:25 AM, Walter Bright wrote:
> But the DIP says const ref is not required. Therefore, copying an lvalue 
> to a temporary cannot be allowed, therefore implicit conversion of 
> lvalues cannot happen.

The biggest reason I see to not worry about const is that we already 
don't for member functions. And the world hasn't ended (yet).

> Then we're faced with the question of if implicit conversion of lvalues 
> is not allowed, should implicit conversion of rvalues be allowed? I'm 
> not so sure it should be. For one thing, a lot of people are confused 
> about lvalues vs rvalues, and would find the difference in behavior 
> puzzling. For another, it can complicate overloading rules. I'd say 
> allowing the conversions needs a strong rationale.

We could certainly start out with no conversions allowed (except you 
MUST allow conversions of compile-time data -- e.g. literals and CTFE 
produced values -- that is very key), and then relax the rules later if 
that's important.


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