With is a Swift micro-library that provides a with statement— which is modeled after the with functionality found in Python, JavaScript, Visual Basic, Object Pascal, Delphi; using found in C#; and also/let found in Kotlin.
With provides a set of overloaded generic free functions that are useful for:
- Object or value initialization and setup in a declarative style (think Swift UI's hierarchical style, but for anything, anywhere).
- Performing multiple operations on an object/value fetched via a method/property, while staying D.R.Y and without needing to create a local var (while still avoiding invoking the method/getter repeatedly).
- Performing calculations with an object/value that only needs to live long enough to be configured and do some calc (and you're only interested in a result object/value).
With provides a free function func with(_ subject: SubjectT, operations: (inout SubjectT) -> Void) -> SubjectT that can be used on any object or value type to do stuff like this:
// initializes a value-type `hitTestOptions` dictionary for use with
// `SCNView`'s `hitTest(…)` with the desired options some of which have
// changed in newer OS versions (which the standard dictionary literal syntax
// can't cleanly do)
let hitTestOptions = with([SCNHitTestOption : Any]()) { o in
o[.boundingBoxOnly] = true
o[.rootNode] = _myRootNode
if #available(iOS 11.0, tvOS 11.0, macOS 10.13, *) {
o[.searchMode] = SCNHitTestSearchMode.all.rawValue
} else {
o[.sortResults] = true
o[.firstFoundOnly] = false
}
}Or like this:
// initializes the object-type `newButton` with title, sizing, styling, etc.
// and adds the view to a superview
let newButton = with(UIButton(type: .system)) { b in
b.titleLabel!.font = .systemFont(ofSize: 13)
b.setTitle("My Button", for: .normal)
b.autoresizingMask = [ .flexibleLeftMargin, .flexibleBottomMargin ]
b.contentEdgeInsets = UIEdgeInsets(top: 6.5, left: 7, bottom: 6.5, right: 7)
with(b.layer) { l in
l.borderWidth = 1.0
l.borderColor = UIColor.white.cgColor
l.cornerRadius = 5
}
b.sizeToFit()
rootViewController.view.addSubview(b)
}With also has an alternate func withMap(_ subject: SubjectT, operations: (inout SubjectT) -> ReturnT) -> SubjectT form that can return an arbitrary value from the closure (instead of the value passed in):
// initializes a `DateFormatter`, configures it, and uses it to calculate a
// `String` which is the only thing we want to hang onto
let dateString = withMap(DateFormatter()) { f in
f.dateStyle = .medium
f.timeStyle = .none
f.locale = Locale(identifier: "en_US")
let currentDate = Date()
return f.string(from: currentDate)
}