Re: Swift generics, circular type declarations, and segfaults, oh my!

[has]

On 06/09/2015 21:50, Charles Srstka wrote:
On Sep 6, 2015, at 3:19 PM, Quincey Morris 
<quinceymor...@rivergatesoftware.com 
<mailto:quinceymor...@rivergatesoftware.com>> wrote:

(But merely defining a protocol for each of your subclasses is not an 
improvement here.)

It does, however, seem to avoid the crash:

class ObjectBase<T> {
required init() {}
}

protocol MyProtocol {
func foo()
func bar()
func baz()
}

class MyObject: ObjectBase<MyProtocol>, MyProtocol {
func foo() { print("foo") }
func bar() { print("bar") }
func baz() { print("baz") }
required init() {}
}

let obj = MyObject()

compiles and runs without errors.


Unfortunately, that doesn't help here since MyObject's methods need to 
return instances of the parameterized type. That's the bit that's 
causing the crashes.

e.g. This test case compiles successfully, but crashes at runtime on 
instantiating YourObject:

    class MyObject<T> {
        required init() {}
        func foo() -> T { return self.dynamicType.init() as! T }
    }

    class YourObject: MyObject<YourObject> {
        required init() {}
    }

    let obj = YourObject()


(It's not a realistic example as I need to return types other than Self, 
but if it had worked I might've used it as a starting point for figuring 
out a solution.)


This expresses my requirements, but won't compile because the compiler 
doesn't know what initializers T implements without more information:

    class MyObject<T> {
        required init() {}
        func foo() -> T { T() }
    }

    class YourObject: MyObject<YourObject> {
        required init() {}
    }

    let obj = YourObject()


But after adding a protocol to supply this information, SourceKit and 
swiftc crash upon reading the code:


    protocol Object {
        init()
    }

    class MyObject<T: Object> {
        required init() {}
        func foo() -> T { T() }
    }

    class YourObject: MyObject<YourObject>, Object {
        required init() {}
    }

    let obj = YourObject()

As suggested, I'm going to write these up as a radar ticket.


Thanks,

has

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