how do people deal with iterating a Swift struct value-type property?

Question

Here\'s an obvious situation that must arise all the time for people:

struct Foundation {
    var columns : [Column] = [Column(), Column()]
}
struct Column :         


        

Answer 1

As of Swift 4, a compromise is to iterate over the indices of a mutable collection instead of the elements themselves, so that

for elem in mutableCollection {
    // `elem` is immutable ...
}

or

for var elem in mutableCollection {
   // `elem` is mutable, but a _copy_ of the collection element ...
}

becomes

for idx in mutableCollection.indices {
    // mutate `mutableCollection[idx]` ...
}

In your example:

for idx in f.columns.indices {
   f.columns[idx].cards.append(Card()) 
}

As @Hamish pointed out in the comments, a future version of Swift may implement a mutating iteration, making

for inout elem in mutableCollection {
   // mutate `elem` ...
}

possible.