Marc Palmer

We can envision constraints being useful for: * Restricting a feature to iPhone or iPad only * Restricting a feature to certain models of Apple Watch only * Restricting a...

Some features require other features to be enabled. This should be evaluated at runtime and not just once when executing `prepare()` on a feature.

You can create problematic feature graphs: ``` Conditional Feature A |--- ConditionalFeature B |--- Feature C ``` Here, if A is not available, C is still always available. This does...

We need this to update UI based on features becoming enabled at runtime after purchase or permissions change

e.g. background/foreground constraints could automatically suppress features that cannot be used in certain modes, without massively affecting the code path. Extensions may be another such "execution mode" where e.g. you...

Some apps may need to have their own permissions declared on features, and their own way of determining and authorising these. e.g. LDAP integration, back end permission schemes etc.

We need to be able to do something like this: ```swift static func constraints(builder ... ) { requirements.iOS = 9 requirements.macOS = "10.12" requirements.permission(.photos) requirements.iOS.atLeast(10) { iOS in iOS.permission(.healthKit) }...