Oh I see, the property itself does not have autoclosure type. Slava
> On Sep 11, 2017, at 3:52 PM, Slava Pestov <spes...@apple.com> wrote: > > No, newValue is a closure here, and valueSource will capture this closure. > When valueSource is evaluated, the original closure will be evaluated. > > Slava > >> On Sep 11, 2017, at 3:11 PM, Hooman Mehr <hoo...@mac.com >> <mailto:hoo...@mac.com>> wrote: >> >> But the expression that is assigned to the property will be eagerly >> evaluated to produce `newValue`. So this will not accomplish what Nevin is >> trying to do. >> >>> On Sep 11, 2017, at 3:08 PM, Slava Pestov via swift-users >>> <swift-users@swift.org <mailto:swift-users@swift.org>> wrote: >>> >>> You can have valueSource store a closure that captures the autoclosure >>> value. For example, >>> >>> set { >>> valueSource = { newValue } >>> } >>> >>> Slava >>> >>>> On Sep 11, 2017, at 11:04 AM, Nevin Brackett-Rozinsky via swift-users >>>> <swift-users@swift.org <mailto:swift-users@swift.org>> wrote: >>>> >>>> Hi, quick question here: >>>> >>>> I have a class with a property that needs to be really *really* lazy. So >>>> lazy, in fact, that when you assign to that property, the class actually >>>> stores a closure of what you assigned, which is only evaluated if and when >>>> you actually attempt to read the property. >>>> >>>> Simplified: >>>> >>>> class Foo { >>>> private var valueSource: () -> Bar >>>> private var valueCache: Bar? >>>> >>>> init(_ v: @escaping @autoclosure () -> Bar) { >>>> valueSource = v >>>> } >>>> >>>> var value: Bar { >>>> get { >>>> if let v = valueCache { return v } >>>> let w = valueSource() >>>> valueCache = w >>>> return w >>>> } >>>> set { >>>> /* ??? */ >>>> } >>>> } >>>> >>>> // I want this function's logic to go in the setter above >>>> func setValue(_ v: @escaping @autoclosure () -> Bar) { >>>> valueSource = v >>>> valueCache = nil >>>> } >>>> } >>>> >>>> The goal is to be able to write things like “someFoo.value = bar1 / bar2” >>>> (or even more complex expressions) and not evaluate them until/unless the >>>> result is actually needed. >>>> >>>> Currently I am using “someFoo.setValue( bar1 / bar2 )”, which is not >>>> nearly as ergonomic as the assignment syntax. So, is there a way to make >>>> this work? >>>> >>>> Nevin >>>> _______________________________________________ >>>> swift-users mailing list >>>> swift-users@swift.org <mailto:swift-users@swift.org> >>>> https://lists.swift.org/mailman/listinfo/swift-users >>>> <https://lists.swift.org/mailman/listinfo/swift-users> >>> >>> _______________________________________________ >>> swift-users mailing list >>> swift-users@swift.org <mailto:swift-users@swift.org> >>> https://lists.swift.org/mailman/listinfo/swift-users >>> <https://lists.swift.org/mailman/listinfo/swift-users> >> >
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