Swift - Type Casting
Per convalidare il tipo di istanza, entra in gioco "Type Casting" nella lingua di Swift 4. Viene utilizzato per verificare se il tipo di istanza appartiene a una particolare superclasse o sottoclasse o è definito nella propria gerarchia.
Il casting di tipo Swift 4 fornisce due operatori "is" per verificare il tipo di un valore e "as" e per eseguire il cast del valore del tipo su un tipo diverso. Il casting del tipo controlla anche se il tipo di istanza segue un particolare standard di conformità del protocollo.
Definizione di una gerarchia di classi
Il casting del tipo viene utilizzato per controllare il tipo di istanze per scoprire se appartiene a un particolare tipo di classe. Inoltre, controlla la gerarchia delle classi e le sue sottoclassi per controllare e lanciare quelle istanze per renderlo come una stessa gerarchia.
class Subjects {
var physics: String
init(physics: String) {
self.physics = physics
}
}
class Chemistry: Subjects {
var equations: String
init(physics: String, equations: String) {
self.equations = equations
super.init(physics: physics)
}
}
class Maths: Subjects {
var formulae: String
init(physics: String, formulae: String) {
self.formulae = formulae
super.init(physics: physics)
}
}
let sa = [ Chemistry(physics: "solid physics", equations: "Hertz"),
Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")]
let samplechem = Chemistry(physics: "solid physics", equations: "Hertz")
print("Instance physics is: \(samplechem.physics)")
print("Instance equation is: \(samplechem.equations)")
let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
print("Instance physics is: \(samplemaths.physics)")
print("Instance formulae is: \(samplemaths.formulae)")
Quando eseguiamo il programma precedente usando playground, otteniamo il seguente risultato:
Instance physics is: solid physics
Instance equation is: Hertz
Instance physics is: Fluid Dynamics
Instance formulae is: Giga Hertz
Tipo di controllo
Il controllo del tipo viene eseguito con l'operatore "is". L'operatore di controllo del tipo "is" controlla se l'istanza appartiene a un particolare tipo di sottoclasse e restituisce "true" se appartiene a tale istanza, altrimenti restituirà "false".
class Subjects {
var physics: String
init(physics: String) {
self.physics = physics
}
}
class Chemistry: Subjects {
var equations: String
init(physics: String, equations: String) {
self.equations = equations
super.init(physics: physics)
}
}
class Maths: Subjects {
var formulae: String
init(physics: String, formulae: String) {
self.formulae = formulae
super.init(physics: physics)
}
}
let sa = [
Chemistry(physics: "solid physics", equations: "Hertz"),
Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz"),
Chemistry(physics: "Thermo physics", equations: "Decibels"),
Maths(physics: "Astro Physics", formulae: "MegaHertz"),
Maths(physics: "Differential Equations", formulae: "Cosine Series")]
let samplechem = Chemistry(physics: "solid physics", equations: "Hertz")
print("Instance physics is: \(samplechem.physics)")
print("Instance equation is: \(samplechem.equations)")
let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
print("Instance physics is: \(samplemaths.physics)")
print("Instance formulae is: \(samplemaths.formulae)")
var chemCount = 0
var mathsCount = 0
for item in sa {
if item is Chemistry {
++chemCount
} else if item is Maths {
++mathsCount
}
}
print("Subjects in chemistry contains \(chemCount) topics and maths contains \(mathsCount) topics")
Quando eseguiamo il programma precedente usando playground, otteniamo il seguente risultato:
Instance physics is: solid physics
Instance equation is: Hertz
Instance physics is: Fluid Dynamics
Instance formulae is: Giga Hertz
Subjects in chemistry contains 2 topics and maths contains 3 topics
Downcasting
Il downcasting del tipo di sottoclasse può essere eseguito con due operatori (as? E as!). 'As?' restituisce un valore facoltativo quando il valore restituisce nil. Viene utilizzato per controllare il downcast riuscito.
'come!' restituisce lo scartamento forzato come discusso nel concatenamento opzionale quando il downcasting restituisce valore nullo. Viene utilizzato per attivare l'errore di runtime in caso di errore di downcast
class Subjects {
var physics: String
init(physics: String) {
self.physics = physics
}
}
class Chemistry: Subjects {
var equations: String
init(physics: String, equations: String) {
self.equations = equations
super.init(physics: physics)
}
}
class Maths: Subjects {
var formulae: String
init(physics: String, formulae: String) {
self.formulae = formulae
super.init(physics: physics)
}
}
let sa = [
Chemistry(physics: "solid physics", equations: "Hertz"),
Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz"),
Chemistry(physics: "Thermo physics", equations: "Decibels"),
Maths(physics: "Astro Physics", formulae: "MegaHertz"),
Maths(physics: "Differential Equations", formulae: "Cosine Series")]
let samplechem = Chemistry(physics: "solid physics", equations: "Hertz")
print("Instance physics is: \(samplechem.physics)")
print("Instance equation is: \(samplechem.equations)")
let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
print("Instance physics is: \(samplemaths.physics)")
print("Instance formulae is: \(samplemaths.formulae)")
var chemCount = 0
var mathsCount = 0
for item in sa {
if let print = item as? Chemistry {
print("Chemistry topics are: '\(print.physics)', \(print.equations)")
} else if let example = item as? Maths {
print("Maths topics are: '\(example.physics)', \(example.formulae)")
}
}
Quando eseguiamo il programma precedente usando playground, otteniamo il seguente risultato:
Instance physics is: solid physics
Instance equation is: Hertz
Instance physics is: Fluid Dynamics
Instance formulae is: Giga Hertz
Chemistry topics are: 'solid physics', Hertz
Maths topics are: 'Fluid Dynamics', Giga Hertz
Chemistry topics are: 'Thermo physics', Decibels
Maths topics are: 'Astro Physics', MegaHertz
Maths topics are: 'Differential Equations', Cosine Series
Typecasting: Any and Any Object
La parola chiave "Any" viene utilizzata per rappresentare un'istanza che appartiene a qualsiasi tipo, inclusi i tipi di funzione.
class Subjects {
var physics: String
init(physics: String) {
self.physics = physics
}
}
class Chemistry: Subjects {
var equations: String
init(physics: String, equations: String) {
self.equations = equations
super.init(physics: physics)
}
}
class Maths: Subjects {
var formulae: String
init(physics: String, formulae: String) {
self.formulae = formulae
super.init(physics: physics)
}
}
let sa = [
Chemistry(physics: "solid physics", equations: "Hertz"),
Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz"),
Chemistry(physics: "Thermo physics", equations: "Decibels"),
Maths(physics: "Astro Physics", formulae: "MegaHertz"),
Maths(physics: "Differential Equations", formulae: "Cosine Series")]
let samplechem = Chemistry(physics: "solid physics", equations: "Hertz")
print("Instance physics is: \(samplechem.physics)")
print("Instance equation is: \(samplechem.equations)")
let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
print("Instance physics is: \(samplemaths.physics)")
print("Instance formulae is: \(samplemaths.formulae)")
var chemCount = 0
var mathsCount = 0
for item in sa {
if let print = item as? Chemistry {
print("Chemistry topics are: '\(print.physics)', \(print.equations)")
} else if let example = item as? Maths {
print("Maths topics are: '\(example.physics)', \(example.formulae)")
}
}
var exampleany = [Any]()
exampleany.append(12)
exampleany.append(3.14159)
exampleany.append("Example for Any")
exampleany.append(Chemistry(physics: "solid physics", equations: "Hertz"))
for print in exampleany {
switch print {
case let someInt as Int:
print("Integer value is \(someInt)")
case let someDouble as Double where someDouble > 0:
print("Pi value is \(someDouble)")
case let someString as String:
print("\(someString)")
case let phy as Chemistry:
print("Topics '\(phy.physics)', \(phy.equations)")
default:
print("None")
}
}
Quando eseguiamo il programma precedente usando playground, otteniamo il seguente risultato:
Instance physics is: solid physics
Instance equation is: Hertz
Instance physics is: Fluid Dynamics
Instance formulae is: Giga Hertz
Chemistry topics are: 'solid physics', Hertz
Maths topics are: 'Fluid Dynamics', Giga Hertz
Chemistry topics are: 'Thermo physics', Decibels
Maths topics are: 'Astro Physics', MegaHertz
Maths topics are: 'Differential Equations', Cosine Series
Integer value is 12
Pi value is 3.14159
Example for Any
Topics 'solid physics', Hertz
AnyObject
Per rappresentare l'istanza di qualsiasi tipo di classe, viene utilizzata la parola chiave "AnyObject".
class Subjects {
var physics: String
init(physics: String) {
self.physics = physics
}
}
class Chemistry: Subjects {
var equations: String
init(physics: String, equations: String) {
self.equations = equations
super.init(physics: physics)
}
}
class Maths: Subjects {
var formulae: String
init(physics: String, formulae: String) {
self.formulae = formulae
super.init(physics: physics)
}
}
let saprint: [AnyObject] = [Chemistry(physics: "solid physics", equations: "Hertz"),
Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz"),
Chemistry(physics: "Thermo physics", equations: "Decibels"),
Maths(physics: "Astro Physics", formulae: "MegaHertz"),
Maths(physics: "Differential Equations", formulae: "Cosine Series")]
let samplechem = Chemistry(physics: "solid physics", equations: "Hertz")
print("Instance physics is: \(samplechem.physics)")
print("Instance equation is: \(samplechem.equations)")
let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
print("Instance physics is: \(samplemaths.physics)")
print("Instance formulae is: \(samplemaths.formulae)")
var chemCount = 0
var mathsCount = 0
for item in saprint {
if let print = item as? Chemistry {
print("Chemistry topics are: '\(print.physics)', \(print.equations)")
} else if let example = item as? Maths {
print("Maths topics are: '\(example.physics)', \(example.formulae)")
}
}
var exampleany = [Any]()
exampleany.append(12)
exampleany.append(3.14159)
exampleany.append("Example for Any")
exampleany.append(Chemistry(physics: "solid physics", equations: "Hertz"))
for print in exampleany {
switch print {
case let someInt as Int:
print("Integer value is \(someInt)")
case let someDouble as Double where someDouble > 0:
print("Pi value is \(someDouble)")
case let someString as String:
print("\(someString)")
case let phy as Chemistry:
print("Topics '\(phy.physics)', \(phy.equations)")
default:
print("None")
}
}
Quando eseguiamo il programma precedente usando playground, otteniamo il seguente risultato:
Instance physics is: solid physics
Instance equation is: Hertz
Instance physics is: Fluid Dynamics
Instance formulae is: Giga Hertz
Chemistry topics are: 'solid physics', Hertz
Maths topics are: 'Fluid Dynamics', Giga Hertz
Chemistry topics are: 'Thermo physics', Decibels
Maths topics are: 'Astro Physics', MegaHertz
Maths topics are: 'Differential Equations', Cosine Series
Integer value is 12
Pi value is 3.14159
Example for Any
Topics 'solid physics', Hertz