On Fri, May 10, 2013 at 6:05 AM, Mark S. Miller <[email protected]> wrote:
> On Fri, May 10, 2013 at 5:55 AM, Mark S. Miller <[email protected]>wrote: > [...] > >> This same abstraction in a Q-like promise system would be written >>> >>> class AsyncTable<t,u> { >>> constructor() { >>> this.m = Map<t,u>(); // encapsulation doesn't matter for >>> this example >>> } >>> set(keyP :Promise<t>, val :u) { >>> keyP.then(key => { this.m.set(key, val) }); >>> } >>> get(keyP :Promise<t>) :Promise<u> { >>> return keyP.then(key => this.m.get(key)); >>> } >>> } >>> >> > > Actually, it's even better: > > > class AsyncTable<t,u> { > constructor() { > this.m = Map<t,u>(); // encapsulation doesn't matter for this > example > } > set(keyP :Promise<t>, val :Ref<u>) { > keyP.then(key => { this.m.set(key, val) }); > } > get(keyP :Promise<t>) :Promise<u> { > return keyP.then(key => this.m.get(key)); > } > } > The way one would actually write in Q is even better class AsyncTable<t,u> { constructor() { this.m = Map<t,u>(); // encapsulation doesn't matter for this example } set(keyP :Ref<t>, val :Ref<u>) { Q(keyP).then(key => { this.m.set(key, val) }); } get(keyP :Ref<t>) :Promise<u> { return Q(keyP).then(key => this.m.get(key)); } } The difference is instructive. The Q version of Postel's law is to either require t or Ref<t>, and to either provide t or Promise<t>. -- Cheers, --MarkM
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