> On Jul 18, 2017, at 3:54 PM, Chris McIntyre <nothingwasdelive...@gmail.com> > wrote: > > Was it ever explained why the syntax is different? >
Oh. I think convenience initializers on classes are marked as such explicitly because convenience vs designated has an effect on the ABI of an initializer, for the purposes of inheritance. With a value type, it doesn’t change anything about how the initializer is used externally. Yeah, probably the AST printer should not print the ‘convenience’ keyword on non-class initializers. Slava > -- > Chris McIntyre > > On Jul 18, 2017, at 6:46 PM, Jens Persson via swift-users > <swift-users@swift.org <mailto:swift-users@swift.org>> wrote: > >> That is not true. Structs can have delegating initializers but they cannot >> be marked with `convenience` (only the initializers of class types can). >> >> This is very clear from both the documentation and the compiler: >> >> (1) The Swift Programming language (Swift 4): >> "Swift defines two kinds of initializers for *class* types to help ensure >> all stored properties receive an initial value. These are known as >> designated initializers and convenience initializers." >> >> (2) The compiler: >> >> struct S { >> var a, b: Int >> init(_ a: Int, _ b: Int) { >> self.a = a >> self.b = b >> } >> convenience init(_ ab: Int) { // <-- Error >> self.init(ab, ab) >> } >> } >> The error message is: >> Delegating initializers in structs are not marked with 'convenience' >> The suggested fix is to remove the word convenience. >> >> Please reread my previous post, perform the steps I describe (looking at >> Quick Help, also try jump to definition for that `init` and you'll see it is >> marked with `convenience` even though it is in a struct), also look at the >> link to the documentation for the Int init, it too is marked with >> convenience, even though Int is a struct. >> >> /Jens >> >> >> On Tue, Jul 18, 2017 at 9:46 PM, Slava Pestov <spes...@apple.com >> <mailto:spes...@apple.com>> wrote: >> Hi Jens, >> >> While I’m not familiar with the integer API in the standard library, structs >> and enums certainly can have convenience initializers. They must delegate to >> another initializer (either convenience or designated) rather than >> initializing the fields of the type one by one. >> >> Slava >> >>> On Jul 18, 2017, at 6:46 AM, Jens Persson via swift-users >>> <swift-users@swift.org <mailto:swift-users@swift.org>> wrote: >>> >>> Start a command line project in Xcode 9 beta 3 and copy paste this single >>> line of code into main.swift >>> >>> let _ = UInt8.init(extendingOrTruncating: UInt64(123456)) >>> >>> Now look at Quick Help while placing the cursor on `init` and then on >>> `extendingOrTruncating`. >>> >>> Note that (and how) the documentation for the initializer differs depending >>> on where you place the cursor. >>> >>> If the cursor is on `init`, the initializer is shown to be a convenience(!) >>> initializer even though structs (such as UInt8) cannot have convenience >>> initializers, right? >>> >>> Even the official documentation for this and several other initializer like >>> eg: >>> https://developer.apple.com/documentation/swift/int/2885075-init >>> <https://developer.apple.com/documentation/swift/int/2885075-init> >>> clearly shows convenience initializers in structs. >>> >>> By the way, .init(extendingOrTruncating:) doesn't show in the list of >>> completions for "UInt8.init" but it does for "UInt8(". >>> >>> >>> Can anyone explain what's going on? >>> >>> Are these known issues that will go away in time for Xcode 9 GM? >>> >>> /Jens >>> >>> _______________________________________________ >>> 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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