draft proposal for Sum Types for D

[Paul Backus]

On Tuesday, 6 December 2022 at 14:44:03 UTC, ryuukk_ wrote:
> On Monday, 5 December 2022 at 18:41:39 UTC, Paul Backus wrote:
>> On Monday, 5 December 2022 at 17:31:11 UTC, Jacob Shtokolov 
>> wrote:
>>> There are other cases where one might need to extend such sum 
>>> types, say, you want to extend error types, etc.
>>
>> The Rust community has come up with a variety of techniques to 
>> handle cases like this using library code. I am confident that 
>> D, with its powerful metaprogramming and reflection, is 
>> capable of handling them just as well, if not better.
>
> Zig and Go does it better, they don't need any "library" 
> "reflection" "metaprogramming", i would never use a language 
> that needs a library to work with errors, it's tasteless

You don't *need* a library, but that doesn't mean it can't be 
useful to have one. For example: in D, you can write all of your 
`throw` and `catch` and `scope (exit)` statements by hand if you 
want, but many users prefer to use library functions like 
[`enforce`][1] and [`ifThrown`][2] to simplify their code.

In fact, it's kind of funny that you bring up Go as an example 
here, because many Go programmers use libraries like 
[`errors`][3] and [`xerrors`][4] that build on top of the 
built-in error handling features to make them more convenient and 
ergonomic. Of course, you don't *need* them, just like you don't 
*need* `enforce` in D, but they are still nice to have.

[1]: https://phobos.dpldocs.info/std.exception.enforce.1.html
[2]: https://phobos.dpldocs.info/std.exception.ifThrown.1.html
[3]: https://pkg.go.dev/errors
[4]: https://pkg.go.dev/golang.org/x/xerrors