> On Jan 22, 2017, at 4:53 PM, Dave Abrahams via swift-evolution > <swift-evolution@swift.org> wrote: > > Sent from my iPad > > On Jan 22, 2017, at 3:15 PM, Chris Lattner <clatt...@nondot.org > <mailto:clatt...@nondot.org>> wrote: > >> >>> On Jan 20, 2017, at 12:22 PM, Dave Abrahams via swift-evolution >>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >>> >>>> >>>> Yeah, maybe there's a more general language feature that could replace >>>> 'fallthrough' here. Instead >>>> of labelling cases, we could support a 'reswitch' statement that >>>> redispatches the switch to the case >>>> matching the operand: >>>> >>>> switch some_value { >>>> case .REFINED: >>>> if !validate(some_value) { return NULL } >>>> reswitch .BASE >>>> >>>> case .BASE: >>>> handle_enum_value(); >>>> } >>> >>> We should just call a spade a spade and spell that "goto" ;-) >> >> Goto has traditionally been used for unstructured control flow, but this >> form is still fully structured. You cannot produce irreducible loops, jump >> into scopes, over declarations, etc. > > It would be useful to know the technical definition of "structured." The fact > is that there's a large category of sensible goto-like jumps that we probably > want to allow and I see no advantage to giving them all distinct names. I > don't believe users will distinguish them. We already have "break looplabel" > and, aside from the label being in the wrong place, it's effectively a goto. > It seems to me we should just have goto and either prohibit the troublesome > uses or give them reasonable semantics. > > I could live with "break" as well as "goto", but it feels a bit like it's > pretending to be something it isn't, and there's the source compatibility > problem with the label position. > > -Dave
I always assumed structured control flow means control only jumps to approved points, not arbitrary statements. Implicitly this is jumping out of a scope to a less-nested scope but never into a more-nested scope. Swift takes this even further: you are limited to early exit of control flow. That’s a lot more restrictive than arbitrary goto. Russ
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