Swift 2.2 Brief Introduction for Experienced Programmer - Part 8 - Generics

Generics 

• Generics are those data type that is unknown. 
• We can create generics in the forms of function, class, methods, structure and enumeration 
• The purpose of creating generic form of function, methods or class is for developer to apply different data type to the function, method or class. 
• To define generics, we need to apply a postfix with a <T> after the function name where T is the placeholder name for generic.

func print10Times<T> (x: T) {
    for _ in 1...10 {
        print(x)
    }
}

let genA = 10
print10Times(genA)
let genB = "Test"
print10Times(genB)
let genC = 12.2
print10Times(genC)

• We can use where after the type name to specify a set of condition or requirement for those data type we can use. 
• We called such condition type constraint. 
• We can demand the generic data type to be subclass from a specific class or to implement certain protocol. 
• In the following example, we will compare if the first input is larger than second input. We use T as generic type. 
• However, without the statement where T: Comparable, the system will give error as we cannot compare generics unless we constraint the generic type to comparable

func isLarger<T where T:Comparable>(first: T, second: T) -> Bool {
    return first > second
}

isLarger(100, second: 20)
isLarger(19972.0212, second: 124.25)

• We can include other constraint such as we can insist that T must conform to a protocol or T and U (second generic type) must be the same. 

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