sumtypes for D

[Steven Schveighoffer]

On 11/28/22 10:37 PM, Paul Backus wrote:
> On Tuesday, 29 November 2022 at 03:03:37 UTC, Steven Schveighoffer wrote:
>>
>> The problem is that there's no syntax to "tail-modify" a type other 
>> than a pointer or an array. This is the biggest problem with properly 
>> using const on ranges (it doesn't prevent using const containers, or 
>> prevent ranges to const data, it just prevents taking a range to a 
>> *mutable container* and iterating it via a const parameter).
>>
>> I think I've been bringing this problem up for 10 years. It would be a 
>> huge win to get it solved.
> 
> The thing is, we pretty much know what the solution is. In the general 
> case, solving this requires user-defined implicit conversions, because 
> in the general case only the user has the knowledge necessary to 
> establish the correspondence between a templated type's *structure* 
> (e.g., "the head-mutable version of `const(Foo!T)`") and its *name* 
> (e.g., `Foo!(const(T))`).

This is not how I would solve it. I would solve it in the general case, 
with a new syntax.

-Steve