Iterating Over Collections

Iterating means visiting every single item in a collection, one after another, usually to do something with each one.

In this page:

.enumerated() pairs each element with its index, letting you access both together inside a for-in loop.

Example: Iterating an Array with enumerated()

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let colors = ["red", "green", "blue"]
for (index, color) in colors.enumerated() {
    print("\(index): \(color)")
}

Iterating a dictionary directly with for-in gives you a tuple of (key, value) for each entry, which can be destructured right in the loop header.

Example: Iterating a Dictionary

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let ages = ["Alice": 30, "Bob": 25]
for (name, age) in ages {
    print("\(name) is \(age)")
}

Common Mistakes

Forgetting that iterating a dictionary gives (key, value) tuples, not just values.
Using an index-based loop when a direct for-in over the collection's elements would be simpler and safer.
Not knowing .enumerated() exists, and manually tracking an index counter variable instead.

Chapter Summary

for-in iterates directly over an array's elements, a set's members, or a dictionary's key-value pairs.
.enumerated() provides both the index and the element together while iterating an array.
Iterating a dictionary yields tuples that can be destructured into separate key and value constants.
Sets iterate in an unspecified order, unlike arrays which preserve insertion order.

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