Doug Gregor cc68b12d1a [SILGen] Initialization of instance properties with property delegates ...

The initialization of an instance property that has an attached
property delegate involves the initial value written on the property
declaration, the implicit memberwise initializer, and the default
arguments to the implicit memberwise initializer. Implement SILGen
support for each of these cases.

There is a small semantic change to the creation of the implicit
memberwise initializer due to SE-0242 (default arguments for the
memberwise initializer). Specifically, the memberwise initializer will
use the original property type for the parameter to memberwise
initializer when either of the following is true:

  - The corresponding property has an initial value specified with the
    `=` syntax, e.g., `@Lazy var i = 17`, or
  - The corresponding property has no initial value, but the property
    delegate type has an `init(initialValue:)`.

The specific case that changed is when a property has an initial value
specified as a direct initialization of the delegate *and* the
property delegate type has an `init(initialValue:)`, e.g.,

```swift
struct X {
  @Lazy(closure: { ... })
  var i: Int
}
```

Previously, this would have synthesized an initializer:

```swift
init(i: Int = ???) { ... }
```

However, there is no way for the initialization specified within the
declaration of i to be expressed via the default argument. Now, it
synthesizes an initializer:

```swift
init(i: Lazy<Int> = Lazy(closure: { ... }))
```

2019-04-23 11:31:59 -07:00

90 KiB

Raw Blame History

View Raw