[swift-evolution] [Review] SE-0030 Property Behaviors

[Brent Royal-Gordon]

> What's to keep us from just treating `initialValue` as similar magic within a behavior declaration? Is it a matter of not wanting to use additional storage if the initial value isn't referenced?

The issue is that some behaviors want to initialize an internal property with an initial value (most of them, but let's use `@synchronized` as an example), some want to re-initialize from that value later (`@lazy`), and some don't want an initial value at all (`@deferred`). Unless we're going to scan the behavior's implementation and try to guess the semantics it wants, we're going to need to declare the desired semantics explicitly. And that means we need a syntax to declare the initial value semantic.

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Brent Royal-Gordon
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