Some type conversion methods in Swift programming are explained in detail
- 2020-05-14 05:00:32
- OfStack
Verify the type 'cast' of an instance in Swift language programming. It is used to check whether an instance type belongs to a particular superclass or subclass or its own hierarchical definition.
Swift type conversion provides two operators: "is" to check the type of the value and "as" to convert the type value to a different type value. The type conversion also checks whether the instance type meets the specific protocol 1 conformance criteria.
Define a class hierarchy
Type conversions are used to check the type of an instance or whether it belongs to a specific type. In addition, examine the class and its subclass hierarchy to examine and transform these instances as one identical hierarchy.
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")
println("Instance physics is: \(samplechem.physics)")
println("Instance equation is: \(samplechem.equations)")
let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
println("Instance physics is: \(samplemaths.physics)")
println("Instance formulae is: \(samplemaths.formulae)")
When we run the above program using playground, we get the following results.
Instance physics is: solid physics
Instance equation is: Hertz
Instance physics is: Fluid Dynamics
Instance formulae is: Giga Hertz
Type checking
Do type checking using the 'is' operator. The 'is' operator checks if the type instance belongs to a particular subtype, and returns' true 'if it belongs to that instance, otherwise returns' 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")
println("Instance physics is: \(samplechem.physics)")
println("Instance equation is: \(samplechem.equations)")
let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
println("Instance physics is: \(samplemaths.physics)")
println("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
}
}
println("Subjects in chemistry contains \(chemCount) topics and maths contains \(mathsCount) topics")
When we run the above program using playground, we get the following results.
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
downcast
Downcast subtypes can have two operators (e.g., as? And as!) . as & # 63; The value is nil and returns an optional value. It is used to check for successful down transitions.
"as!" Returns a forced unwrapping, such as an optional chain, and a downconversion returns an nil value. It is used to trigger runtime errors in the event of a downshift failure
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")
println("Instance physics is: \(samplechem.physics)")
println("Instance equation is: \(samplechem.equations)")
let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
println("Instance physics is: \(samplemaths.physics)")
println("Instance formulae is: \(samplemaths.formulae)")
var chemCount = 0
var mathsCount = 0
for item in sa {
if let print = item as? Chemistry {
println("Chemistry topics are: '\(print.physics)', \(print.equations)")
} else if let example = item as? Maths {
println("Maths topics are: '\(example.physics)', \(example.formulae)")
}
}
When we run the above program using playground, we get the following results.
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
Type conversion: any with any object
To indicate that an instance belongs to any type, including a function type, use the "Any" keyword
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")
println("Instance physics is: \(samplechem.physics)")
println("Instance equation is: \(samplechem.equations)")
let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
println("Instance physics is: \(samplemaths.physics)")
println("Instance formulae is: \(samplemaths.formulae)")
var chemCount = 0
var mathsCount = 0
for item in sa {
if let print = item as? Chemistry {
println("Chemistry topics are: '\(print.physics)', \(print.equations)")
} else if let example = item as? Maths {
println("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:
println("Integer value is \(someInt)")
case let someDouble as Double where someDouble > 0:
println("Pi value is \(someDouble)")
case let someString as String:
println("\(someString)")
case let phy as Chemistry:
println("Topics '\(phy.physics)', \(phy.equations)")
default:
println("None")
}
}
When we run the above program using playground, we get the following results.
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
To represent a class instance of any type, use the AnyObject "keyword
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")
println("Instance physics is: \(samplechem.physics)")
println("Instance equation is: \(samplechem.equations)")
let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
println("Instance physics is: \(samplemaths.physics)")
println("Instance formulae is: \(samplemaths.formulae)")
var chemCount = 0
var mathsCount = 0
for item in saprint {
if let print = item as? Chemistry {
println("Chemistry topics are: '\(print.physics)', \(print.equations)")
} else if let example = item as? Maths {
println("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:
println("Integer value is \(someInt)")
case let someDouble as Double where someDouble > 0:
println("Pi value is \(someDouble)")
case let someString as String:
println("\(someString)")
case let phy as Chemistry:
println("Topics '\(phy.physics)', \(phy.equations)")
default:
println("None")
}
}
When we run the above program using playground, we get the following results.
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