> 31 maj 2016 kl. 21:37 skrev Chris Lattner <[email protected]>:
>
>> On May 31, 2016, at 6:32 AM, David Rönnqvist via swift-evolution
>> <[email protected]> wrote:
>> Lazy evaluation when assigning static variables
>> Introduction
>> Both stored type properties (static) and lazy stored properties (lazy var)
>> are lazily initialized. However, they have different initialization behavior
>> in that stored type properties evaluate even when assigning them a new value.
>>
>> The following code will print "static", but not "lazy":
>>
>> class Foo {
>> static var bar: String = {
>> print("static")
>> return "Default"
>> }()
>>
>> lazy var baz: String = {
>> print("lazy")
>> return "Lazy"
>> }()
>> }
>>
>> Foo.bar = "Set" // this evaluates the initial value of `bar` before setting
>> a new value
>>
>> let foo = Foo()
>> foo.baz = "Set" // this doesn't evaluate `baz` before setting a new value
> This seems like a step in the right direction, but may not big a step far
> enough. Keep in mind that “static” and global variables are quite different
> than lazy variables, both in terms of implementation and behavior but also in
> terms of planned future direction.
>
> “lazy” is almost certainly to be replaced by property behaviors in the
> future, making them a library defined feature whose behavior can be changed
> arbitrarily, and can hopefully have useful additional functionality like a
> “reset()” method added to them. Global variables are currently not like
> that: their behavior is defined by compiler magic instead of by property
> semantics.
>
> If the goal was to remove magic from the compiler, then a possible direction
> would be to do something like:
>
> 1) Introduce a new declmodifier named something like “atomiclazy”.
> 2) Disallow global and static variables, unless they are explicitly marked
> atomiclazy (compiler would provide a fixit hint to suggest this).
> 3) Replace the atomiclazy magic with a property behavior when they exist.
>
> In this model, you’d presumably have the choice about atomiclazy or lazy when
> setting up either a static or a local property.
>
> -Chris
>
Did I understand it correctly that, under such a proposal, there would be no
compiler magic for global properties and instead both global, type, and
instance properties would be controlled by property behaviors (or
lazy/atomiclazy until they are replaced by property behaviors)?
`lazy` having he current a behavior of lazy properties (no threading
guarantees, not evaluating on assignment),
`atomiclazy` having the current behavior of static properties (guaranteed to
only evaluate once when accessed from multiple threads, evaluating even on
assignment)
- David
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