Re: Implicit conversion from 'Ok' to 'Result' type when returning functions

[Nicholas Wilson via Digitalmars-d-learn]

On Sunday, 21 May 2017 at 08:44:31 UTC, David  Zhang wrote:

Hi,

I was reading a bit about this in Rust, and their enum type. I was wondering if this is replicate-able in D. What I've got right now is rather clunky, and involves using

     `typeof(return).ok` and `typeof(return).error)`.

While that's not too bad, it does involve a lot more typing, and thus more area for human error.

If you're not familiar with the Result and Option types, it allows you to do something like this:

---
Result!(string, ErrorEnum) someFunction(...)
{
    return Ok("Hello!");
}

Result!(string, ErrorEnum) someFunction2(...)
{
    return Error(ErrorEnum.dummyError);
}
---

I'm not entirely sure it's possible... but I figured I might give it a try.

have free functions

 Result!(T, ErrorEnum) ok(T)(T t) { return Result(t); }
 Result!(T, ErrorEnum) error(T)(ErrorEnum e) { return Result(e); }

then go

if (!foo)
    return ok(42);
else
    return error(Error.fooHappened);