-preview=in might break code

[Steven Schveighoffer]

On 10/2/20 6:11 PM, Walter Bright wrote:
> On 10/2/2020 10:31 AM, Steven Schveighoffer wrote:
>> And this might not be true on a different compiler.
> 
> This is looking like a serious problem.

I was wrong about this case, because it's a dynamic array (which is 
specifically carved out as an exception). Indeed, there seem to be quite 
a few exceptions carved out, presumably to make existing code behave 
reasonably.

But this could be true for another type that isn't in the exception 
categories. Potentially, a compiler can decide to make the following not 
true, while others say it is true:

alias A = void delegate(in long);
alias B = void delegate(const long);

static assert(is(A : B));

-Steve