Alternatives to exceptions for error handling

[Roman Kashitsyn]

In the video from DConf 2020 about @live functions 
(https://youtu.be/XQHAIglE9CU) Walter mentioned that all @live 
functions are nothrow.  He also thinks that exceptions are 
obsolete.

I've been programming in Google's C++, Go & Rust for quite a few 
years and I couldn't agree more with this assessment.  Error 
handling is a very important part of program engineering, and 
having errors reflected in function return types is very useful 
in practice.  This helps a lot with constructing correct programs.

So my question is: does/will D provide support for alternative 
approaches to error handling?  In practice, this typically 
includes 2 things:

1. A sum type that contains either a result or an error. Like 
Result in Rust or Expected that Andrei proposed for C++.  It's 
easy to implement in D, but having this in Phobos would be nice.

2. Some kind of syntactic sugar for propagating errors upstream 
(? macro in Rust, check/handle proposal in Go 
https://go.googlesource.com/proposal/+/master/design/go2draft-error-handling.md, an ugly macro in C++, etc.).