Accessing map values in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a map in Go?

A map in Go is a collection of key-value pairs where each key is unique and is used to access its corresponding value.

beginner

How do you access a value from a map in Go?

You access a value by using the key inside square brackets after the map variable, like: value := myMap[key].

beginner

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

Go returns the zero value of the map's value type (e.g., 0 for int, "" for string) if the key is not found.

intermediate

How can you check if a key exists in a Go map when accessing its value?

You can use the two-value assignment: value, ok := myMap[key]. The 'ok' is true if the key exists, false otherwise.

intermediate

Why is it useful to check if a key exists in a Go map before using its value?

Because accessing a non-existent key returns a zero value, which might be misleading. Checking existence helps avoid bugs by confirming the key is present.

How do you access the value for key "name" in a Go map called 'person'?

A person["name"]

B person.name

C person->name

D person.get("name")

In Go, map values are accessed using square brackets with the key inside, like person["name"].

What does Go return if you access a key that does not exist in a map?

A An error is thrown

B The zero value of the map's value type

C nil

D The last inserted value

Go returns the zero value for the map's value type if the key is missing, without throwing an error.

Which syntax correctly checks if a key exists in a Go map?

A value, ok := myMap[key]

B value := myMap[key]

C exists := myMap.contains(key)

D if myMap[key] != nil

The two-value assignment 'value, ok := myMap[key]' lets you check if the key exists with 'ok'.

What type is the variable 'ok' when checking map key existence in Go?

A int

B string

C bool

D interface{}

'ok' is a boolean that is true if the key exists, false otherwise.

Why might you want to check if a key exists before using its value from a map?

A To avoid runtime errors

B To delete the key

C To get the zero value

D To confirm the key is present and avoid using default zero values mistakenly

Checking existence helps avoid confusion caused by zero values returned for missing keys.

Explain how to access a value from a map in Go and how to check if the key exists.

Think about how you get a value and also know if it is really there.

Describe what happens when you access a key that does not exist in a Go map and why checking existence is important.

Consider what Go returns and how that might confuse your program.