switch case let ... where
Swift โฉ Pattern Matching โฉ Sentence Patterns โฉ
case: pattern matching.
let: variable binding.
where: condition on bound variable.
๐พ ็จๅผ๏ผ replit
import Foundation // for URL
// -------------
// Media
// -------------
/// enum with associated values
enum Media {
case book(title: String, author: String, year: Int)
case movie(title: String, director: String, year: Int)
case website(title: String, url: URL, year: Int)
}
extension Media {
/// media title
var title: String {
switch self {
// 2: โญ switch case let
// (pattern matching + data binding)
// --------------------------------------------------------
// - labels can be omitted
// - `case let .book(x, y, z) == case .book(let x, let y, let z)`
// - `case let .book(x, _, _) == case .book(let x, _, _)
case let .book (t, _, _): return t
case let .movie (t, _, _): return t
case let .website(t, _, _): return t
}
}
/// media title too
var title2: String {
switch self {
// 3: โญ switch case let
// (pattern matching + binding multiple cases)
// -----------------------------------------------
case
.book (let t, _, _),
.movie (let t, _, _),
.website(let t, _, _): return t
}
}
func isPublished(after year: Int) -> Bool {
switch self {
// 5: โญ switch case let ... where
// -------------------------------
// (pattern matching + data binding + condition on binding)
// - Note:
// โข `case .a(let x), .b(let x) where x > 0` is NOT equivalent to
// `case .a(let x) where x > 0, .b(let x) where x > 0`
// โข `case let .a(x), .b(x) where x > 0` WON'T compile.
// "โ๏ธ error: `x` must be bound in every pattern"
case
// for demo of `where` clause only, not recommended
.book(_, _, let y) where y > year,
.movie(_, _, let y) where y > year,
.website(_, _, let y) where y > year:
return true
// recommended way
// case let .book(_,_,y), .movie(_,_,y) ... : return y > year
default: return false
}
}
}Last updated