Enumerate through array of structs

Question

Take a look at this code:

struct Person {
    var name: String
    var age: Int
}

var array = [Person(name: "John", age: 10), Person(name: "Apple", age: 20), Person(name: "Seed", age: 30)]

//for item in array { item.name = "error: cannot assign to property: 'item' is a 'let' constant" }
array[0].name = "Javert" //work fine.

I'm trying to change property's value of a struct inside a loop.

Of course I can change Person to class and it works just fine. However, I don't understand why item is a le.

Oh, I just figured this out, for item in... just created an copied of actual object inside array, that means it is automatically declared as a let constant.

So that's why I cannot change its properties value.

My question is, beside changing Person to class, how can I change Person's properties inside a loop ?

Edit:

Thank to @Zoff Dino with the original for index in 0..<array.count answers.

However, this is just a simplified question.

What I want to archive is using higher-order functions with array of structs, like:

array.each { item in ... }.map { item in ... }.sort { } ...

Code Different · Accepted Answer · 2015-08-15 03:10:16Z

4

The old school for i in ... will do the job just fine:

for i in 0..<array.count {
    array[i].name = "..."
}

Edit: higher order function you said? This will sort the array descendingly based on age:

var newArray = array.map {
        Person(name: "Someone", age: $0.age)
    }.sort {
        $0.age > $1.age
    }

print(newArray)

edited Aug 15, 2015 at 3:10

answered Aug 15, 2015 at 2:54

Code Different

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1 Comment

Pham Hoan Over a year ago

Ya, thank you, I forgot that :D But this is just a simplified question. What I want to archive is using higher-order functions with array of structs, like: array.each { item in ... }.map { item in ... }.sort { } ...

Qbyte · Accepted Answer · 2016-05-31 16:57:51Z

2

If you only want to change some properties of the elements you can use map and return a mutated copy of it:

array.map{ person -> Person in
    var tempPerson = person
    tempPerson.name = "name"
    return tempPerson
}.sort{ ... }

edited May 31, 2016 at 16:57

answered Aug 15, 2015 at 16:09

Qbyte

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2 Comments

Qbyte Over a year ago

@PhamHoan Considering performance I should be very efficient since structs/value types can be copied very fast. A slightly more efficient version would be a for in loop over the indices and mutate the elements directly because no additional array has to be created. So for small arrays I wouldn't consider performance too much.

Qbyte Over a year ago

@adnako Thank you. I've updated my solution. The reason was that Swift 2.2 disallows var parameters.

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