Swift How to for-in loop over references

Question

I have quite a few similar UILabels I setup in code. In Objective-C I would do something like this (pseudo-code):

@property (nonatomic, strong) UILabel *l1, *l2, *l3, *l4, *l5, *l6, *l7, *l8, *l9;
...
l1 = [[UILabel alloc] init]; 
l2 = [[UILabel alloc] init];
l3 = [[UILabel alloc] init];
...
NSArray *lbls = @[l1, l2, l3, l4, l5, l6, l7, l8, l9];
for(UILabel *l in lbls) {
   l.textColor = [UIColor redColor];
   l.hidden = YES;
   ...
   [self.addSubview:l];
}

How would I do this in Swift? How can I pass the reference to a variable in a for in loop? The only option I found was to make a function with an inout parameter, but that splits my code into different areas.

Thanks

Why do you have 10 label variables instead of one array variable in the first places? — Sulthan, Jan 22 '17 at 17:35
fair point ;-) am going to implement something like vacawama suggested — Joseph, Jan 23 '17 at 07:07

score 2 · Accepted Answer · edited May 23 '17 at 10:29

You do it in Swift exactly the same way you do it in Objective-C:

let lbls = [l1, l2, l3, l4, l5, l6, l7, l8, l9]
for l in lbls {
   l.textColor = .red
   l.isHidden = true
   self.addSubview(l)
}

This works the same way it did in Objective-C because UILabel is a class, which is a reference type. This means that, in a very real sense, l is a pointer every bit as much in Swift as in Objective-C (where the pointer-ness is made explicit by the UILabel* syntax).

Extra Credit

On the other hand, as long as you didn't intend to write all those changes back into lbls, you could also make this work even if this were a value type. You would have to assign l into a var inside the loop in order to change it.

So, let's suppose for purposes of illustration that we have a struct here. Then you would say:

let myArrayOfStructs = [l1, l2, l3, l4, l5, l6, l7, l8, l9]
for s in myArrayOfStructs {
   var s = s // make a version of `s` we can modify
   s.someProperty = newValue
   self.someMethod(s)
}

But, as I say, this would not write back the changes into the contents of the original array. Still, if your only purpose is to configure each s and then hand it off to some other method, you might not care about that.

I wish extra credit could be given. This two variation answer deserves it. THANK YOU! — Confused, Jan 22 '17 at 17:47
@Hamish Yes, I became shy of that syntax because for a while they threatened to remove it. — matt, Jan 22 '17 at 18:05

score 1 · Answer 2 · answered Jan 22 '17 at 17:30

1

It can be pretty much exactly the same.

I would do it this way...

labels.forEach {
    $0.backgroundColor = .red
    view.addSubview($0)
}

answered Jan 22 '17 at 17:30

Fogmeister

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vacawama · Answer 3 · 2017-01-22T18:14:38.100

1

Why have 9 different variables to hold the labels? You can start with all of them in an array and refer to them as labels[0], labels[1], ... , labels[8] when you need to access them individually:

// Create 9 UILabels and store them in [UILabel]
var labels = (1...9).map { _ in UILabel() }

...

for l in labels {
    l.textColor = .red
    l.isHidden = true
    self.addSubview(l)
}

edited Jan 22 '17 at 18:14

answered Jan 22 '17 at 17:52

vacawama

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good point. where as matt's answer answers my original question - I will go forward with this solution. +1 – Joseph Jan 23 '17 at 07:10

Swift How to for-in loop over references

3 Answers3