[swift-evolution] [Proposal] Property behaviors

Ben Langmuir blangmuir at apple.com
Thu Jan 14 11:49:09 CST 2016

Hey Joe,

Just a small bug report:
A deferred initializer is used only after the initialization of the behavior's state. A deferred initializer cannot be referenced until the behavior's storage is initialized. A property using the behavior can refer to self within its initializer expression, as one would expect a lazy property to be able to.

  var behavior deferredInit: Int {
    eager initializer: Int
Presumably “eager” should be “deferred” here.

> On Jan 13, 2016, at 2:07 PM, Joe Groff via swift-evolution <swift-evolution at swift.org> wrote:
> Thanks everyone for the first round of feedback on my behaviors proposal. I've revised it with the following changes:
> - Instead of relying on mapping behaviors to function or type member lookup, I've introduced a new purpose-built 'var behavior' declaration, which declares the accessor and initializer requirements and provides the storage and behavior methods of the property. I think this gives a clearer design for authoring behaviors, and allows for a more efficient and flexible implementation model.
> - I've backed off from trying to include 'let' behaviors. As many of you noted, it's better to tackle immutable computed properties more holistically than to try to backdoor them in.
> - I suggest changing the declaration syntax to use a behavior to square brackets—'var [behavior] foo'—which avoids ambiguity with destructuring 'var' bindings, and also works with future candidates for behavior decoration, particularly `subscript`.
> Here's the revised proposal:
> https://gist.github.com/jckarter/50b838e7f036fe85eaa3
> For reference, here's the previous iteration:
> https://gist.github.com/jckarter/f3d392cf183c6b2b2ac3
> Thanks for taking a look!
> -Joe
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> swift-evolution at swift.org
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