Coding Explorer Blog

Writing Class Initializers

So, I have mentioned a few times about initializers on this blog.  I want to talk today about writing and using initializers for classes, later we can talk a bit more about how they are different for value types like structs or enumerations.

Initializers do exactly what is sounds like they do, they initialize your instances and get them ready to use.  Specifically, before an object can be used, it must set all of its stored properties to valid values.  This can be handled in one of three ways:

• Give them default values in their property definition
• Set them during the initializer
• Declare them as optionals

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In my previous post Classes In Swift — An Introduction, I mentioned that I should probably use an enumeration to denote what the status of my Message was (whether it was sent, received, or read).  Now, I could write a full MessageStatus enumeration with its own file that could be imported into any project, and that would work.  But really, this status is only supposed to talk about my custom class here, about my “Message” class.  Why go through all of the hassle to make this some generic MessageStatus enumeration that could be used on messages completely unrelated to my Message class?

This is exactly where we would want to use a nested type!
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Classes are a very important part of any Object Oriented language, and Swift is no exception.  When I explain classes to people, I usually think of one to describe a car.  That’s a bit cliché, and done in a WWDC video, so let’s do something different.

Creating A Class in Swift

Let’s say we are making a chat program in Swift.  It primarily sends messages in text format, but occasionally, it will also send images.  We will first create our more general Message class, which we will specialize into those different formats later:

class Message {
    //Message code goes here
}

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The Swift dictionary is another very useful type of collection in Swift.  Like arrays (which you can read more about in my post Arrays and their Methods in Swift), you access them via subscripts usually.  Unlike Swift arrays though, these subscripts accept many more values besides Ints.  There are some limitations, but it nonetheless gives you a lot more capability than arrays if you need they key used to look it up to be something other than a number.  We will also go over some of the methods for dictionaries as well, but there are not nearly as many as for arrays.
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We aren’t done with closures quite yet.  We learned last time about how to write and compress closure expressions in the post Closure Expressions in Swift.  Now, how about we talk about making functions that take them as parameters or return them!  I am still very new to closures, so I do not fully know the power that these hold, so my examples will only show the tip of the iceberg.  When I understand more, I will definitely come back and share, but for the moment, I have to know how to get started with them, so let’s see how that goes.
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