A minimal (but hacky) way to add support for void to Result
originally posted bitcoin#27632 (comment)

…al_str>` with `util::Result`

8aa8f73 refactor: Replace std::optional<bilingual_str> with util::Result (Ryan Ofsky)
5f49cb1 util: Add void support to util::Result (MarcoFalke)

Pull request description:

  Replace uses of `std::optional<bilingual_str>` with `util::Result` as suggested bitcoin/bitcoin#25648 (comment), bitcoin/bitcoin#27632 (comment), bitcoin/bitcoin#27632 (comment), bitcoin/bitcoin#24313 (comment)

ACKs for top commit:
  MarcoFalke:
    very nice ACK 8aa8f73 🏏
  TheCharlatan:
    ACK 8aa8f73
  hebasto:
    ACK 8aa8f73, I have reviewed the code and it looks OK.

Tree-SHA512: 6c2f218bc445184ce93ec2b907e61666a05f26f2c9447f69fcb504aa8291b0c693d913f659dfd19813a9e24615546c72cbe2ca419218fd867ff0694c4a1b6a30

… with `util::Result`

8aa8f73 refactor: Replace std::optional<bilingual_str> with util::Result (Ryan Ofsky)
5f49cb1 util: Add void support to util::Result (MarcoFalke)

Pull request description:

  Replace uses of `std::optional<bilingual_str>` with `util::Result` as suggested bitcoin#25648 (comment), bitcoin#27632 (comment), bitcoin#27632 (comment), bitcoin#24313 (comment)

ACKs for top commit:
  MarcoFalke:
    very nice ACK 8aa8f73 🏏
  TheCharlatan:
    ACK 8aa8f73
  hebasto:
    ACK 8aa8f73, I have reviewed the code and it looks OK.

Tree-SHA512: 6c2f218bc445184ce93ec2b907e61666a05f26f2c9447f69fcb504aa8291b0c693d913f659dfd19813a9e24615546c72cbe2ca419218fd867ff0694c4a1b6a30

…ions

A minimal (but hacky) way to add support for void to Result
originally posted bitcoin/bitcoin#27632 (comment)

Summary:
> Useful to encapsulate the function result object (in case of having it) or, in case of failure, the failure reason.
>
> This let us clean lot of boilerplate code, as now instead of returning a boolean and having to add a ref arg for the
> return object and another ref for the error string. We can simply return a 'BResult<Obj>'.
>
> Example of what we currently have:
> ```
> bool doSomething(arg1, arg2, arg3, arg4, &result, &error_string) {
>     do something...
>     if (error) {
>         error_string = "something bad happened";
>         return false;
>     }
>
>     result = goodResult;
>     return true;
> }
> ```
>
> Example of what we will get with this commit:
> ```
> BResult<Obj> doSomething(arg1, arg2, arg3, arg4) {
>     do something...
>     if (error) return {"something happened"};
>
>     // good
>     return {goodResult};
> }
> ```
>
> This allows a similar boilerplate cleanup on the function callers side as well. They don't have to add the extra
> pre-function-call error string and result object declarations to pass the references to the function.

bitcoin/bitcoin@7a45c33

----

> Prepare BResult for non-copyable types

bitcoin/bitcoin@fa8de09

----

> Refactor: Replace BResult with util::Result
>
> Rename `BResult` class to `util::Result` and update the class interface to be
> more compatible with `std::optional` and with a full-featured result class
> implemented in bitcoin/bitcoin#25665. Motivation for
> this change is to update existing `BResult` usages now so they don't have to
> change later when more features are added in #25665.
>
> This change makes the following improvements originally implemented in #25665:
>
> - More explicit API. Drops potentially misleading `BResult` constructor that
>   treats any bilingual string argument as an error. Adds `util::Error`
>   constructor so it is never ambiguous when a result is being assigned an error
>   or non-error value.
>
> - Better type compatibility. Supports `util::Result<bilingual_str>` return
>   values to hold translated messages which are not errors.
>
> - More standard and consistent API. `util::Result` supports most of the same
>   operators and methods as `std::optional`. `BResult` had a less familiar
>   interface with `HasRes`/`GetObj`/`ReleaseObj` methods. The Result/Res/Obj
>   naming was also not internally consistent.
>
> - Better code organization. Puts `src/util/` code in the `util::` namespace so
>   naming reflects code organization and it is obvious where the class is coming
>   from. Drops "B" from name because it is undocumented what it stands for
>   (bilingual?)
>
> - Has unit tests.

bitcoin/bitcoin@a23cca5

----

> util: Add void support to util::Result
>
> A minimal (but hacky) way to add support for void to Result
> originally posted bitcoin/bitcoin#27632 (comment)

bitcoin/bitcoin@5f49cb1

----

This is a partial backport of [[bitcoin/bitcoin#25218 | core#25218]], [[bitcoin/bitcoin#25594 | core#25594]], [[bitcoin/bitcoin#25721 | core#25721]] and [[bitcoin/bitcoin#25977 | core#25977]]

The wallet use cases in the first 3 pull requests are not yet applicable to Bitcoin ABC due to missing dependencies.
The `std::optional<bilingual_str>` use cases from [[bitcoin/bitcoin#25977 | core#25977]] will be backported in their own diff.

Test Plan: `ninja && ninja check`

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14991