Thanks for getting this landed! Hooray for better error handling! \o/
On Tue, Dec 20, 2016 at 5:46 AM, Jan de Mooij <jdemo...@mozilla.com> wrote:
> Hi all,
>
> A few weeks ago we added mozilla::Result<V, E> to MFBT [0][1]. I was asked
> to inform dev-platform about this, so here's a quick overview.
> mozilla::Result<V, E> is based on Rust's Result type [2]. It contains
> either a success value of type V or an error value of type E. For example,
> a function Foo that returns an `int` on success or some `Error` (enum,
> pointer, etc) on failure, would have this signature:
>
> Result<int, Error> Foo();
>
> mozilla::Ok is an empty struct that can be used when a function doesn't
> return anything on success:
>
> Result<Ok, Error> Bar() { ... return Ok(); }
>
> The MOZ_TRY(expr) macro is similar to Rust's try! macro: if `expr` is an
> error it propagates it to the caller, else it continues:
>
> Result<V, E> Baz() { MOZ_TRY(Bar()); ... }
>
> There's also a MOZ_TRY_VAR macro that can be used when you want to store
> the return value on success. Result has isOk(), isErr(), unwrapOk(),
> unwrapErr() methods that do what you'd expect. It also has the
> MOZ_MUST_USE_TYPE annotation, so the static analysis builds will complain
> if you ignore the return value of a function that returns Result.
>
> Internally, Result uses mozilla::Variant, but there are some cases that can
> be stored more efficiently. For instance, Result<Ok, Error&> just stores an
> Error* pointer and Ok is represented as nullptr. This is more efficient and
> will also make it easier to call functions that return Result from JIT
> code. The documentation [3] has more info.
>
> The long-term plan is to use Result in SpiderMonkey, to simplify our
> error/OOM handling [4][5].
>
> Many thanks to Jason Orendorff (jorendorff) for doing most of the work by
> writing the initial Result patches, and to Jeff Walden (Waldo) for his
> thorough code reviews.
>
> Jan
>
> [0] https://bugzilla.mozilla.org/show_bug.cgi?id=1283562
> [1] https://searchfox.org/mozilla-central/source/mfbt/Result.h
> [2] https://doc.rust-lang.org/std/result/
> [3]
> https://searchfox.org/mozilla-central/rev/cc2a84852bd4e6f6d8d4d5b17b8382
> bb5d005749/mfbt/Result.h#148-158
> [4] https://bugzilla.mozilla.org/show_bug.cgi?id=1277368
> [5] https://searchfox.org/mozilla-central/source/js/public/Result.h
> _______________________________________________
> dev-platform mailing list
> dev-platform@lists.mozilla.org
> https://lists.mozilla.org/listinfo/dev-platform
>
_______________________________________________
dev-platform mailing list
dev-platform@lists.mozilla.org
https://lists.mozilla.org/listinfo/dev-platform
