iPhone Development

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Porting to Swift from Objective-C

Finally its time to take swift language on a serious note. All the examples in the blogs have been converted to swift language. With me having worked with a bit of Java(Android), Python and javascript, I thought i could speed up my learning by porting one of the existing Objective-C project where I can touch upon all most often used elements

Note: This is not a Introduction to Swift programming post. I would suggest you read this, if you are an seasoned Objective-C developer and want to see a sneak peak of what Swift has to offer you.

In this post, I will be walking you through the differences/modifications I found when porting from Objective-C to Swift ( Don’t mistake this with Convert-to-swift feature in Xcode). The differences would be more of a design / semantical in nature and not one-to-one mapping of syntax. Fo e.g. I will not say that to declare a class, you use class keyword  in swift instead of @interface in Objective-C. These differences are nothing new in any object oriented languages. However, Objective-C being dynamic typed language, It need a perspective change to program in swift, especially if you have been coding in Objective-C for a long time. 

 

#1 You don’t have to subclass all your classes from NSObject

“NSObject is root of all the classes. It provides methods for things like alloc, init and release. Objective-C is all about sending messages to other objects – so NSObject exists to provide this basic functionality” – from http://stackoverflow.com/a/12991946/623569

#2 Immutability is let, Mutability is var. Always start with ‘let’

Its takes time to get used to using let or var keywords to declare a variable, and it takes more time to know that mentioning Data type is not mandatory. But the key thing, is swift compiler does not complain if you declare a variable using var and does not modify it. This means, that you will end up with swift compiler generating a lot of code to support mutability of these variables which directly affect overall performance.

@iDeekshi got me a nice tip – Start with declaring a variable as let and let the compiler complain when it is mutated.

#3 Yet another block syntax 

It took a lot of time for me to practice the block syntax in Objective-C. In swift, it looks like I am back to square one. Flower braces ‘{‘ starting before the parameter declaration, and writing the function definition after ‘in’ keyword is something I am still getting used to.  Here is it how it looks:

{

[capture list] (parameters) -> Return Type  in

<code>

..

..

#4 Use === to compare two object pointers

Comparing two object pointers studentObj == otherStudentObject will now need to be studentObject === otherStudentObject. Its a good move.

#5 You no longer need NSDictionary to send more than one value. Swift introduces Tuples to return multiple values

This has been a long time ask from me. I am glad we finally have it. You can create a type with just defining all the values and its types in a parenthesis as show below

func getMinAndMax( numbers : [Int] ) -> (min : Int, max : Int ){ 

   var max = numbers[0] , min = numbers[0] 

 ..

 ..

return (min,max)

}

 

#6 Initialize all your variables in the class before calling super init.

class Person{

var name : “”

init() {

name = “<unknown>”

}

}

class Teacher : Person{

var subjects : [String]

init() {

 //we have to initialize the subjects before calling super init

subjects = [“English” , “Kannada”]

super.init()

}

}

This is not the complete list. I have only picked those which I thought had a striking difference from what we are used to while programming in Objective-C. 

Let me know your experiences while porting Objective-C to swift code through comments.

Happy Coding 🙂

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