C++ pattern matching is coming

[Timon Gehr]

On 10/24/22 01:42, Walter Bright wrote:
> On 10/23/2022 4:02 PM, Timon Gehr wrote:
>> I don't expect it to be "finalized" very soon. It lacks 
>> expressiveness, which will be improved by small, incremental changes.
> 
> The changes have been bug fixes. The concept has held up well.
> 

As soon as people try to use it in production they will run into some 
issues with expressiveness. For example, DIP1000 does not even support 
storing objects with different lifetimes in different fields of the same 
struct. (Real case that came up on Discord today.)

The underlying issue is that DIP1000 lacks a modular way to track 
different lifetimes. E.g., DIP100 does not allow having an array 
allocated on a region allocator, containing references pointing to 
objects allocated on a distinct region allocator with correct lifetime 
tracking. As soon as you store things in the array and want to get them 
back out, if it works at all, their lifetimes will be limited by the 
lifetime of the region allocator that backs the array storage, even if 
their own allocator actually is longer-lived.

DIP1000 is very keen to conflate different lifetimes and to cut the 
longer one off based on the shorter one.