Subscripts?, have you ever listened about this?, probably yes, if not, believe me, you have used them.
I'll make this post really basic to get involved with this.
If you are reading this, you are interested on iOS development or just Swift stuffs.
What are subscripts?, when I said that you have used them, it is because they are on Arrays
, Dictionaries
, Sets
.
At the time we do something like this
var characters = ["Jill", "Claire", "Carlos", "Leon", "Ada"]
characters[0] // <- Here we are using our subscript
I'm a Resident Evil fan in case it wasn't clear 😁
Just think of subscripts
as overloading the []
operator, it is an easy way to be familiar with them, and they are useful to create shortcuts for accessing elements.
This can be used on
collections
,enumerations
,structures
andclasses
How to use subscripts
The subscript
syntax is really easy, it is just like this.
subscript(parameters) -> ReturnType {
get { ... }
set(newValue) { ... }
}
The nice part is that you may be related with this syntax, it looks like a function
's signature combined with computed properties
.
Let's make a list of the stuffs you CAN and you CAN'T do
- You CAN use variadic parameters.
- You CAN'T use
inout
parameters. - You CAN'T use
default
parameters. - You CAN'T
throw
errors. - You CAN make it
read-only
, making theset
optional. - You CAN omit
newValue
Now let's do the funny part! the example!
Example
Just because of my love for Resident Evil games, let's create a Character
class to be related with games!
struct Character {
let name: String
let costume: Costume
enum Costume: String {
case `default`
case stars
case re3Style
}
}
let jill = Character(name: "Jill Valentine", costume: .re3Style)
Now, let's try to get the name of our character
object, of course we could just do it like with dot-notation
but c'mon, this is a subscript
post, so we want to read it like this jill["costume"]
If we try to use that line we will receive a very beautiful error! 🤯.
"Value of type 'Character' has no subscripts"
Now, let's fix it extending our struct
in order to add our subscript
extension Character {
subscript(key: String) -> String? {
switch key {
case "name":
return name
case "costume":
return costume.rawValue
default:
return nil
}
}
}
Now, with this code we can call our line again
jill["costume"] // <- Now we got "re3Style"
There you go! You have created your own custom subscript!, of course this is not all, but I want to keep this post as simple as I can, so later on, I'll create more about subscripts
Happy coding devs!
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