How is the value obtained from a dictionary starting from the key and passing through its hash function?

In iOS (and in programming in general), a dictionary is implemented as a hash table. To get a value by key, several steps occur:

1. Hashing the key — a hash function is called, which converts the key into a numerical value (hash).

2. Determining the index in the bucket array — the hash code is used to compute an index in the array where the dictionary's elements are stored. This is usually done using the modulo operation with the array size.

3. Searching for the element in the bucket — since different keys can have the same hash (collisions), the bucket may contain a list or tree of elements. The elements are iterated over with a check for key equality.

4. Returning the value — if the key is found, the associated value is returned.

In Swift, for example, a dictionary is implemented exactly this way, but the details are hidden from the developer. When using dict[key], all these steps are performed automatically.

Example in Swift:

let dict = ["apple": 1, "banana": 2]
if let value = dict["apple"] {
    print(value) // 1
}

Thus, retrieving a value starts with computing the hash of the key, which allows for quick lookup of the desired element in the data structure.