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);