Swift Dictionary Collections

Swift dictionaries allow data to be stored and managed in the form of key-value pairs. Dictionaries fulfill a similar purpose to arrays, except each item stored in the dictionary has a unique key associated with it, which can be used to reference and access the corresponding value. To be precise, the key is unique to the particular dictionary object. Currently, only String, Int, Double, and Bool data types are suitable for use as keys within a Swift dictionary.

Swift dictionary initialization

A dictionary is a data type designed specifically to hold multiple values in a single unordered collection. Each item in a dictionary consists of a key and an associated value. The data types of the key and value elements type may be declared using type annotation or left to the compiler to identify using type inference.

A new dictionary may be initialized with a collection of values (referred to as a dictionary literal) at creation time using the following syntax:

var variableName: [key type: value type] = [key 1: value 1, key 2: value2 …. ]

The following code creates a new dictionary assigned to a variable (thereby making it mutable) that is initialized with four key-value pairs in the form of ISBN numbers acting as keys for corresponding book titles:

var bookDict = ["100-432112" : "Wind in the Willows",
                "200-532874" : "Tale of Two Cities",
                "202-546549" : "Sense and

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