1 can already be accomplished by moving the custom initializer into an extension.
Jon > On Jun 21, 2017, at 7:42 PM, Mike Kluev via swift-evolution > <[email protected]> wrote: > > hi. here are a few somewhat related initializer proposals for your > consideration. > they are designed as "opt-ins" so shall not break existing code. > > ***** proposal 1 ***** > have an ability to keep default initializers in structs > > struct S { > var int: Int > var float: Float > var bool: Bool > } > > here default initializer is currently generated: > > struct S { > var int: Int > var float: Float > var bool: Bool > > // autogenerated: > // init(int: Int, float: Float, bool: Bool) { > // self.int <http://self.int/> = int > // self.float = float > // self.bool = bool > // } > } > > so we can write: > > let s = S(int: 0, float: 0, bool: false) > > so far so good. now i want to add a "convenience" initializer. i don't want > the default initializer to go away though: > > struct S { > var int: Int > var float: Float > var bool: Bool > > /* convenience */ init(x: Int) { > self.init(int: 0, float: 0, bool: false) // *** ERROR. this > initializer is gone > } > } > > let s = S(x: 0) > let s = S(int: 0, float: 0, bool: false) // *** ERROR. this initializer is > gone > > this may be convenient in some cases but not others. > proposal: introduce an opt-in construct to keep the default initializer > intact: > > struct S { > var int: Int > var float: Float > var bool: Bool > > default init // explicit opt-in. suggest a better name > > /* convenience */ init(x: Int) { > self.init(int: 0, float: 0, bool: false) // still ok > } > } > > let s = S(x: 0) // ok > let s = S(int: 0, float: 0, bool: false) // still ok > > > ***** proposal 2 ***** > have the default initializer to have default nil values for all optional > parameters in structs > > struct S { > var int: Int > var float: Float? > var bool: Bool > > // autogenerated: > // init(int: Int, float: Float? = nil, bool: Bool) { > // self.int <http://self.int/> = int > // self.float = float > // self.bool = bool > // } > } > > in the extreme case: > > struct S5 { > var int: Int? > var float: Float? > var bool: Bool? > > // autogenerated: > // init(int: Int? = nil, float: Float? = nil, bool: Bool? = nil) { > // self.int <http://self.int/> = int > // self.float = float > // self.bool = bool > // } > } > > usage: > S(float: 3) > S() > S(int: 0, float: 0, bool: false) > > note that this is still "opt-in" as the old code will be using the full form > anyway and not break. > > ***** proposal 3 ***** > introduce a similar opt-in default initialiser for classes: > > class C { > var int: Int > var float: Float? > var bool: Bool > } > > let c = C(int: 0, float: 0, bool: false) // *** ERROR > > class C { > var int: Int > var float: Float? > var bool: Bool > > default init // explicit opt-in. suggest a better name > > // this is autogenerated: > // init(int: Int, float: Float? = nil, bool: Bool) { > // self.int <http://self.int/> = int > // self.float = float > // self.bool = bool > // } > } > > let c = C(int: 0, bool: false) // ok > > > ***** question 4 ***** > > this one is not a proposal, rather a question. probably there is a good > reason for it, i just want to know it: why there is no default initializer > for classes similar to what we have for structs? > > > ================================= > thoughts and comments on any of these? > > Mike > > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution
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