[swift-evolution] [Pitch] Unifying init parameters with properties

[David Sweeris]

I think I like the idea... However IMHO this really feels like something that should be part of a macro system, not a "proper" language feature.

- Dave Sweeris

> On Apr 16, 2016, at 08:17, Jonathan Hull via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Since we know the types of the properties, how about we replace the type in the signature with either an indication that the property should be automatically set, or better yet, the property which should be set:
> 
> class Foo
> {
> 	let foo : String
> 	let bar : String
> 	let barCount : Int
> 	let baz : Int
> 
> 	init(foo: self.foo, bar: self.bar, baz: self.baz)
> 	{
> 		self.barCount = bar.characters.count
> 	} 
> }
> 
> That way you don’t always have to have the init’s parameter names match the names of the properties they set (even though they often would).  We could also allow a leading dot as a shorthand for ‘self.’
> 
> 	init(foo: .foo, bar: .bar, baz: .baz)
>  
> I think I like explicit ‘self.’ better, but that may just be my preference.  In either case, the generated interface would show the actual type.
> 
> 	// init(foo: String, bar: String, baz: Int)
> 
> Thanks,
> Jon
> 
>> This is a common pattern for initialisers at the moment:
>> 
>> class Foo
>> 
>> {
>> 
>> let foo : String
>> 
>> let bar : String
>> 
>> let barCount : Int
>> 
>> let baz : Int
>> 
>> 
>> init(foo: String, bar: String, baz: Int)
>> 
>> {
>> 
>> self.foo = foo
>> 
>> self.bar = bar
>> 
>> self.baz = baz
>> 
>> barCount = bar.characters.count
>> 
>> }
>> 
>> }
>> 
>> This involves a lot of using 'self.'. For those who prefer not to use
>> 'self.' explicitly everywhere, this is probably the main place it gets
>> used. It's a lot of boilerplate code.
>> 
>> How would it be if, like default variables, we could pack some of that
>> information into the argument tuple, and unify parameters with properties
>> immediately?
>> 
>> class Foo
>> 
>> {
>> 
>> let foo : String
>> 
>> let bar : String
>> 
>> let barCount : Int
>> 
>> let baz : Int
>> 
>> 
>> init(self.foo: String, self.bar: String, self.baz: Int)
>> 
>> {
>> 
>> barCount = bar.characters.count
>> 
>> }
>> 
>> }
>> 
>> Less boilerplate, more focus on the properties which need to be generated.
>> 
>> Thoughts?
> 
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