draft proposal for Sum Types for D

[Steven Schveighoffer]

On 11/29/22 3:04 PM, Walter Bright wrote:
> On 11/29/2022 9:14 AM, Steven Schveighoffer wrote:
>> 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.
>>
> I thought it mentioned that copy constructors, postblits, and 
> destructors are not allowed.

It mentions postblit and destructors *on the union itself* are not 
allowed. It says nothing on field declarations.

These make sense given that a union itself cannot know what the actual 
data stored its (unless you embed the type somehow in the data itself). 
However, a sumtype would not have that problem.

Honestly, the trickiest parts of making a library sumtype *are* the 
lifetime issues. I would hope the builtin thing would solve this for us.

-Steve