Naming and Clarity

// GOOD — "for" distinguishes key lookup from index lookup
dictionary.removeValue(forKey: key)

// BAD — is key the value or the lookup key?
dictionary.remove(key)

// GOOD — "for" clarifies the relationship
extension List {
    func member(for key: Key) -> Value?
}

// BAD — what is "key" relative to the list?
extension List {
    func member(_ key: Key) -> Value?
}

// GOOD — preposition clarifies direction
view.fade(from: previousColor)

// BAD — is this the target or the source?
view.fade(previousColor)

// GOOD
allViews.remove(cancelButton)

// BAD — "Element" repeats the type constraint
allViews.removeElement(cancelButton)

// GOOD
let result = parser.parse(data)

// BAD — "Data" is already the parameter type
let result = parser.parseData(data)

// GOOD
func move(to point: CGPoint)

// BAD — "point" is already in the type
func moveToPoint(_ point: CGPoint)

// GOOD — describes the role
var greeting: String
var bodyText: String
let widthConstraint: NSLayoutConstraint
func restock(from supplier: Warehouse)

// BAD — describes the type
var string: String
var text: String
let constraint: NSLayoutConstraint
func restock(from warehouse: Warehouse)

// GOOD
protocol Container {
    associatedtype Element
    associatedtype Index
}

// BAD — names the constraint, not the role
protocol Container {
    associatedtype ItemType
    associatedtype IntegerIndex
}

// GOOD — role words compensate for weak types
func addObserver(_ observer: NSObject, forKeyPath path: String)
func fill(with color: UIColor, alpha: Double)
func setTag(_ tag: Int, for view: UIView)

// BAD — weak types make the call site opaque
func add(_ object: NSObject, for string: String)
func fill(with any: UIColor, _ value: Double)
func set(_ value: Int, for object: UIView)

// GOOD — return context clarifies weak type
func maximumScore() -> Int
func playerName() -> String

// BAD — generic return with no context
func value() -> Int
func name() -> String

// GOOD — common word suffices
skin                // not "epidermis"
beginners           // not "neophytes"

// GOOD — term of art is precise and necessary
func sin(_ angle: Double) -> Double  // "sine" is the term of art

// GOOD — Array is the established term
struct Array<Element> { ... }

// BAD — "List" means something different in CS (linked list)
struct List<Element> { ... }  // if it's really an array

// GOOD
var backgroundColor: UIColor
var characterIndex: Int

// BAD
var bgColor: UIColor
var charIdx: Int

// GOOD — matches existing Swift/Cocoa convention
Array, Dictionary, Set       // not Vector, Map, HashSet
sin(x), cos(x)              // not sine(x), cosine(x)