Swift - dictionary with array - get reference to array

Question

I currently have this code:

var dic = [String: [String]]() 

if (dic.index(forKey: key) != nil){
    dic[key]?.append(m)
}
else {
    dic[key] = [m]
}

However, in dic.index(forKey: key) and dic[key]?.append(m) I calculate the key twice.

Is there a possibility to do something like this?:

var dictKeyVal = &dic[key]
if (dictKeyVal != nil) {
    dictKeyVal?.append(m)
}
else {
    dic[key] = [m]
}

where I get the reference to array at key or nil if there is no key

**Tip:** You should never do this in Swift `if (dictKeyVal != nil)`. — Rakesha Shastri, Nov 22 '18 at 10:17

score 5 · Accepted Answer · answered Nov 22 '18 at 10:10

5

You can simply use a default value for the subscript and your whole code will be simplified to this:

var dic = [String: [String]]()
dic[key, default: []].append(m)

answered Nov 22 '18 at 10:10

Dávid Pásztor

Default should be [m] – Joakim Danielson Nov 22 '18 at 10:11
@JoakimDanielson nope, that would result in `dic[key] = [m,m]` instead of the desired `dic[key] = [m]` in case there was no value for `key`. – Dávid Pásztor Nov 22 '18 at 10:13
Sorry, now I get it. Neat solution btw. – Joakim Danielson Nov 22 '18 at 10:15

1 Answers1