Swift - Mutability of Dictionaries

Introduction

When creating a dictionary, its mutability depends on whether you use either the let or the var keyword.

If you use the let keyword, the dictionary is immutable: its size cannot be changed after it has been created, as you are creating a constant.

If you use the var keyword, the dictionary is mutable: its size can be changed after its creation, as you are creating a variable.

Demo

var products = [
     "Apple" : ["iPhone", "iPad", "iPod touch"],
     "Google" :  ["Nexus S", "Nexus 4", "Nexus 5"],
     "Microsoft" : ["Lumia 920", "Lumia 1320","Lumia 1520"]
]

products["Apple"] = ["A", "B", "C"]

var models = products["Apple"]
if models != nil {
    print(models![0])   //iPhone
}

Result

Related Topic

• Dictionaries
• Get to know Dictionaries
• Retrieving Elements from a Dictionary
• Checking the Size of a Dictionary
• Modifying an Item in the Dictionary
• Removing an Item from the Dictionary
• Iterating over a Dictionary
• Creating an Empty Dictionary
• Testing Dictionaries for Equality
• Copying The Behavior Of Arrays And Dictionaries

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