draft proposal for Sum Types for D

[Steven Schveighoffer]

On 11/29/22 1:26 AM, Walter Bright wrote:
> Go ahead, Make My Day! Destroy!
> 
> https://github.com/WalterBright/DIPs/blob/sumtypes/DIPs/1NNN-(wgb).md

In Prior work, I suggest adding 
[TaggedAlgebraic](https://github.com/s-ludwig/taggedalgebraic) and I 
also suggest reading about how it works. I find it much nicer to use 
than std.sumtype.

In the DIP, it says that "Member functions of field declarations are 
restricted the same way union member functions are." What does this 
mean? I can't find any information on this in the spec.

An example of what is not allowed would be helpful.

-Steve