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
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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.
- Bouke
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