> On Aug 28, 2016, at 3:44 AM, Bouke Haarsma via swift-evolution > <[email protected]> wrote: > > On 2016-08-26 15:39:05 +0000, Félix Cloutier via swift-evolution said: > > Hi all, > > Currently, a function that throws is assumed to throw anything. There was a > proposal draft last December to restrict that. The general idea was that > you'd write, for instance: > > > enum Foo: ErrorProtocol { > case bar > case baz > } > > func frob() throws Foo { > throw Foo.bar // throw .bar? > } > > If you `catch Foo` (or every case of Foo), now that the compiler can verify > that your catch is exhaustive, you no longer have to have a catch-all block > at the end of the sequence. > > This impacts the metadata format and has implications on resilience, which > leads me to believe that the discussion could qualify for the phase 1 of > Swift 4. If this is the case, I'd be interested in pulling out the old > discussions and seeing where we left that at. > Félix > > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution > > > Hi, > > Shouldn't the compiler be able to infer the types thrown, and thus whether > all types have been thrown? The general idea being that the following would > be valid: > > enum Foo: Error { > case bar > case baz > } > > func hello() throws { // inferred to throw only "Foo.bar" > throw Foo.bar > } > > func world() throws { // inferred to throw only "Foo.baz" > throw Foo.baz > } > > func galaxy() throws { // inferred to throw only "Foo.baz" > do { > try hello() > } catch Foo.bar { > // ... > } > // catch is exhaustive, no catch-all clause needed > > try world() > } > > func universe() { // all errors are handled, no 'throws' declaration needed > do { > try galaxy() > } catch Foo.baz { > // .. > } > // catch is exhaustive, no catch-all clause needed > } > > Now for clarity one could add the type information as per your proposal, but > wouldn't be necessary as the compiler would infer it itself. > > Either way a +1 from me, as the current model forces one to catch-all errors, > even the ones you did not expect to be thrown. Thus potentially hiding > programming errors.
I would definitely give a strong -1 to any proposal that tried to have the compiler infer this, because it would break the ability for a future revision of galaxy() to add a new error that could potentially be thrown. If we’re going to add typed throws, they should only be added if deliberately specified by the developer. Charles
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