On Tue, Dec 20, 2016 at 10:31 AM, Ehsan Akhgari <[email protected]>
wrote:
> > Result<V, E> Baz() { MOZ_TRY(Bar()); ... }
>
> I have one question: what is Bar() expected to return here?
Result<T, F> where F is implicitly convertible to E.
An E type,
> or a type that's implicitly convertible to E
> (<https://searchfox.org/mozilla-central/rev/cc2a84852bd4e6f6d8d4d5b17b8382
> bb5d005749/mfbt/Result.h#198>
> suggests that this is the case), or something else?
The implicit conversion solves a real problem. Imagine these two operations
have two different error types:
MOZ_TRY(JS_DoFirstThing()); // JS::Error&
MOZ_TRY(mozilla::pkix::DoSecondThing()); // pkix::Error
We don't want our error-handling scheme getting in the way of using them
together. So we need a way of unifying the two error types: a shared base
class, perhaps, or a variant.
Experience with Rust says that MOZ_TRY definitely needs to address this
problem somehow. C++ implicit conversion is just one way to go; we can
discuss alternatives in the bug.
-j
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