So my code hasn't crashed, but this feels like it shouldn't be safe, but I can't find a clear answer in the swift docs. I'm iterating over a dictionary with a for-in loop and removing those elements if not found in a reference array. I'm wondering if this is safe, and if so, why?
func cleanupETADictionary(trips: [Int64]){
for (tripId, _) in etaDictionary{
if !trips.contains(tripId){
etaDictionary.removeValue(forKey: tripId)
}
}
}
The iteration does not work like you're thinking it does. Your iterated etaDictionary is a copy of the original. Dictionaries are value types in Swift.
Clear example:
var dictionary = [1: 1, 2: 2, 3: 3, 4: 4, 5: 5]
for kvp in dictionary {
dictionary = [:]
print(kvp)
print(dictionary.count)
}
outputs:
(key: 5, value: 5)
0
(key: 3, value: 3)
0
(key: 4, value: 4)
0
(key: 1, value: 1)
0
(key: 2, value: 2)
0
There's a name for your for loop, though; it is called filter. Use it instead.
func cleanupETADictionary(trips: [Int64]){
etaDictionary = etaDictionary.filter { trips.contains($0.key) }
}