Hello, I am trying to understand logic behind unwrapping optionals... I know, I have to unwrap dictionary key/value pair because swift always return an optional value

why does not the same apply to arrays? what is the reason behind this logic?

let names = ["Carl", "Amy"]
let dictionary = ["wtf": "what true false"]

print(dictionary["wtf"])  //Optional("what true false")
print(names[0])           //Carl

thanks

Because you declared your array with non-optional Strings. On the other hand, the key you ask for in the dictionary couldn't exist.

Declare your Array with var names: [String?] = [nil, "Carl", "Amy"] and you should see a different result. With your definition of names Swift declares your Array implicitly as [String].

@Hatsushira yeah, I understand this, but... My question is more like what thinking is behind this architecture of swift... Why is dicitonary always optional but array only if i declare it? Like those two feels kinda same in some ways (both conform to Collection protocol), yet array items are not optional by default.

A dictionary is an array of key: value pairs. If you try accessing a dictionary for a key that does not exist it will return nil.

For return type consistency (think of it as a return value from a function) the type returned from a dictionary has to be an optional. Whether it is a real value or nil, the return has to handle both.

In the case of arrays, you define whether the elements are optional or not. You will either allow a nil value, or not. Up to you.

Try this in Playground. Note: for the print statements you will see warnings that Int? has been coerced as Any.

var myDictionary: [String: Int] = [:]
myDictionary["One"] = 1
print (myDictionary["One"])
myDictionary["One"] = 2
print (myDictionary["One"])
print (myDictionary["Two"])
print (myDictionary)

You will see that the first print with the key "One" will print out 1, and the second print will be 2 (because the key was found in the the dictionary and the corresponding value was changed to 2.

The third print statement uses a key that does not exist in myDictionary, and so the value returned is nil.

The final print statement shows the whole of myDictionary, which in this case is ["One": 2].