Swift - dictionary with array - get reference to array [duplicate]

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
– Rakesha Shastri, Commented Nov 22, 2018 at 10:17

David Pasztor · Accepted Answer · 2018-11-22 10:10:23Z

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, 2018 at 10:10

David Pasztor

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3 Comments

Default should be [m]

@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.

Sorry, now I get it. Neat solution btw.