[swift-evolution] Type-annotated throws

[Adrian Zubarev]

@Anton: We still allowed to discuss it now. :) That won’t bother people that much.

Just a side note without reading all the stuff going on here.

As much as I would love to have some type safety error handling, I do believe it should be optional in first place.

Image some scenario like this:

func foo() throws AError {}
func boo() throws BError {}
func zoo() throws CError {}

// We also need some design to handle all errors at once:
func handle() rethrows AError & BError & CError -> ReturnType {}

// As you can imagine the line might become really long and ugly looking
// Merging with existential syntax or typealias?
func handle() rethrows Any<AError, BError, CError> -> ReturnType {}

typealias ABCError = AError & BError & CError

func handle() rethrows ABCError -> ReturnType {}

// But sometime you don't really care which error type might be thrown and your API handles it with some other convention (docs?)
func handle() rethrows -> ReturnType {
    try foo()
    try boo()
    try zoo()
    return ReturnType()
}
A mix of a type safe and the current error handling mechanism would be great, but not just the type safe (except we’ll get AnyError, where just re-/throws might be a shorthand form for re-/throws AnyError).
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