Map use cases in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a map in Go?

A map in Go is a built-in data type that stores key-value pairs. It allows you to quickly look up a value by its key, similar to a dictionary in real life where you find a word's meaning by looking it up.

beginner

How do you declare and initialize a map in Go?

You declare a map using the syntax: var m map[string]int. To initialize it, use m = make(map[string]int) or declare and initialize together with m := map[string]int{"key": 1}.

beginner

What happens if you try to access a key that does not exist in a Go map?

If you access a key that does not exist, Go returns the zero value for the map's value type. For example, if the map stores integers, it returns 0. You can also check if the key exists using the two-value assignment: value, ok := m[key].

beginner

Name a common use case for maps in Go.

Maps are commonly used to count occurrences, like counting how many times each word appears in a text. They are also used for fast lookups, caching data, and grouping related information by keys.

beginner

How do you delete a key-value pair from a map in Go?

You use the built-in delete function: delete(m, key). This removes the key and its value from the map.

How do you check if a key exists in a Go map?

A value, ok := m[key]

B exists := m.contains(key)

C if m[key] != nil

D m.hasKey(key)

In Go, you use the two-value assignment: value, ok := m[key]. The variable ok is true if the key exists.

What is the zero value returned when accessing a missing key in a map of type map[string]int?

A 0

B "" (empty string)

C nil

D false

For int values, the zero value is 0, so accessing a missing key returns 0.

Which function initializes a map in Go?

A init()

B new()

C make()

D create()

The make() function initializes maps, slices, and channels in Go.

How do you remove a key-value pair from a map?

A m.remove(key)

B delete(m, key)

C m.pop(key)

D m.clear(key)

The built-in delete(m, key) function removes a key and its value from the map.

Which of these is NOT a typical use case for maps?

A Caching data

B Fast data lookup by key

C Counting word frequencies

D Storing ordered lists

Maps do not maintain order, so they are not used for storing ordered lists.

Explain how you would use a map in Go to count how many times each word appears in a sentence.

Think about how a map can store words as keys and counts as values.

Describe how to safely check if a key exists in a Go map and handle the case when it does not.

Remember the special syntax Go provides for map lookups.