100 + Que/Ans Series , I will post a continue series on iOS Interview questions from a basic concept to advance .
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“You will get answer for given question in first few line , and after that there will be some insights and key points about that question .”
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1. What is Type Inference ?
In short its an ability of swift . You dont always need to write types of variables and constant you making in your code . For example :
// swift know its Int type
var age = 40 // Int
// You dont need to tell them always like below
var age : Int = 40 2. What is Generics ?
Generic code enables you to write flexible, reusable functions and types that can work with any type, subject to requirements that you define.
Understanding it with an example :
Suppose you want to swap to values of type Int , lets write a non-generic functions :
func swapTwoInts(_ a: inout Int, _ b: inout Int) {
let temporaryA = a
a = b
b = temporaryA
}var num1 = 4
var num2 = 5
swapTwoInts(&num1 , &num2)
Now , suppose you want to swap two double values or two string values , you will need to write another function for that , because the above function is accepting only for Int type .
What if we have a function which accept any type of values and swap them , this is what generic do .
Now lets do the same thing with a generic function :
func swapTwoValues<T>(_ a: inout T, _ b: inout T) {
let temporaryA = a
a = b
b = temporaryA
}
var num1 = 3
var num2 = 4
swapTwoValues(&num1 , &num2)var str1 = "sdf"
var str2 = "dafdf"
swapTwoValues(&str1 , &str2)
Now you can swap any type of values , you dont need to write different different function to swap different different type of values.
- T is a placeholder , called as type parameter .
We use array in swift which is also a generic type
- Array <Element> , Dictionary<Key , Value>
3. What are Protocols ?
Its a blueprint of methods, properties, and other requirements that suit a particular task and it could adopted by a class , structure or enumeration .
Protocol does not include any implementation !!!!
Type which is adopting the protocol , should have all the methods which are present in given protocol . And this action is called conforming protocol .
Its syntax looks like :
protocol Vehicle {
func accelerate()
func stop()
}class Unicycle : Vehicle {
var peddling = false
func accelerate(){
peddling = true
}
func stop() {
peddling = false
}
}
4. What are Tuples ?
Sometimes data comes in pairs or triplets. An example of this is a pair of (x, y) coordinates on a 2D grid. Similarly, a set of coordinates on a 3D grid is comprised of an x-value, a y-value and a z-value. In Swift, you can represent such related data in a very simple way through the use of a tuple.
let coordinates: (Int, Int) = (2, 3)5. What about Mutability in Swift ?
Constant(let) are constant in swift and variable(var) varies .
6. What are Subscripts ?
With subscripts you can quickly access the member elements of collections.
A subscript consists of:
- The name of the collection, such as
scores - Two square brackets
[and] - A key or index inside the brackets
By default, you can use subscripts with arrays, dictionaries, collections, lists and sequences. You can also implement your own with the
subscriptfunction.
subscript(parameterList) -> ReturnType {
get {
// return someValue of ReturnType
}
set(newValue) {
// set someValue of ReturnType to newValue
}7. What is an Optional ?
Optionals are Swift’s solution to the problem of representing both a value and the absence of a value. An optional is allowed to hold either a value or nil.
8. In what ways you could Unwrap an optional ?
We can unwrap any optional in following ways :
- By Optional Binding
- By Force Unwrapping
- By Guard Statement
- By Nil Coalescing
Optional Binding (If let)
Its simplest way to do unwrap an optional .
var authorName : String? = "Mohd Yasir"if let authorName == authorName {
print("Author name is \(authorName)")
else{
print("No Author Name")
}
By Force Unwrapping
To force unwrap , we use “!” .
var authorName : String? = "Mohd Yasir"
print("Auhor name : \(authorName!)")Guard Statement
Sometimes you want to check a condition and only continue executing a function if the condition is true, such as when you use optionals. Imagine a function that fetches some data from the network. That fetch might fail if the network is down. The usual way to encapsulate this behavior is using an optional, which has a value if the fetch succeeds, and nil otherwise.
Swift has a useful and powerful feature to help in situations like this: the guard statement.
func testingGuard( _ name : String?){
guard let unrappedname = name else {
print("You dont entered any name")
return
}
print("Hello , \(unrappedname)")
}Nil Coalescing
let name = String? = nil
let unwrappedName = name5 ?? "Unkonwn"9. What kind of memory allocations takes place in Swift ?
In short Stack and Heap
When you create a reference type such as class, the system stores the actual instance in a region of memory known as the heap. Instances of a value type such as a struct resides in a region of memory called the stack .
10. What is the difference between stack and heap memory ?
- The system uses the stack to store anything on the immediate thread of execution; it is tightly managed and optimized by the CPU. When a function creates a variable, the stack stores that variable and then destroys it when the function exits. Since the stack is so strictly organized, it’s very efficient, and thus quite fast.
- The system uses the heap to store instances of reference types. The heap is generally a large pool of memory from which the system can request and dynamically allocate blocks of memory. Lifetime is flexible and dynamic. The heap doesn’t automatically destroy its data like the stack does; additional work is required to do that. This makes creating and removing data on the heap a slower process, compared to on the stack.
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