Count the Number of Properties in a Struct

Yes! It is possible

_{Photo by Mirko Blicke on Unsplash}

Difficulty: Beginner | Easy | Normal | Challenging This article has been developed using Xcode 12.0.1, and Swift 5.3

Terminology:

Property: An association of a value with a class, structure or enumeration Struct: An object defined in Swift, using pass by value semantics

Prerequisites

• Be able to create a basic Swift application

There are plenty of reasons why we might want to know the number of properties within a given struct.

The real example (for those interested)

I wanted to insert fields into an SQL table. I could read the columns from the table using PRAGMA table_info, and then I want to insert the data a client would like into that table from a generic struct - with the idea that our code can work with any SQL table and any client providing any struct. Phew!

The example code

There can be a simple struct that stores an animal

struct Animal {
    var name: String
    var species: String
    var owner: String
}

which can then be set up as an instance of (in this case) an Animal.

var derek = Animal(name: "Derek", species: "Dog", owner: "Kim")

We can then set up a Mirror

var mirror = Mirror(reflecting: derek)

and then the values can be printed to the console

print (mirror.children.map{ $0.value })
// ["Derek", "Dog", "Kim"]

also going further we can count the number of children, and therefore the number of properties

print (mirror.children.count)
// 3

this also works with a struct, which is excellent!

var ahmed = Person(name: "Ahmed", age: 21)
print (mirror.children.count)

The optional question

Optional properties are still properties, and therefore still count (for want of a better word) for this count.

So an optional does indeed contribute to the mirror.children.count

Conclusion

You can read more about reflection in Swift.

This is a feature of Swift that has helped me to produce code to solve a specific problem that I had. For you? This is a great feature of Swift that you should have in your coding toolkit.

Stay safe, stay coding.

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