Maps

Question	Click to View Answer
What does the following code print? package main import "fmt" func main() { numbers := make(map[string]int) numbers["one"] = 1 numbers["ten"] = 10 numbers["twenty"] = 20 fmt.Println(numbers) }	`map[one:1 ten:10 twenty:20]` is printed. The `numbers` variable is initally assigned to an empty map that's declared to have string keys and integer values. Three key / value pairs are then added to the `numbers` map. The `numbers` map is then printed.
What does the following code print? numbers := map[string]int{ "one": 1, "ten": 10, "twenty": 20, } fmt.Println(numbers)	`map[ten:10 twenty:20 one:1]` is printed. Maps are unordered, so the ordering of the key / value pairs may be different when this map is printed on your machine. Maps can be created with a shorthand syntax that's similar to the shorthand syntax used to create arrays and slices.
What does the following code print? numbers := map[string]int{ "one": 1, "ten": 10, "twenty": 20, } fmt.Println(len(numbers))	`3` is printed. The `numbers` map contains 3 key / value pairs. The `len()` function returns the number of key / value pairs in a map.
What does the following code print? numbers := map[string]int{ "one": 1, "ten": 10, "twenty": 20, } delete(numbers, "ten") fmt.Println(numbers)	`map[twenty:20 one:1]` is printed. The `delete()` function can be used to delete a key / value pair from a map.
What does the following code print? places := make(map[string]int) fmt.Println(places["boo"])	`0` is printed. The `places` map is declared to have string keys and integer values. The length of `places` is zero (i.e. `len(places == 0`). When a key doesn't exist in a map, the zero value of the value type is returned. In this example, the value type is an integer and the zero value of an integer is 0, so 0 is returned for the "boo" key that doesn't exist in the map.
What does the following code print? countryCodes := map[string]string{ "93": "Afghanistan", "374": "Armenia", "61": "Australia", } country, ok := countryCodes["61"] fmt.Println(country, ok)	`Australia true` is printed. The `countryCodes` map contains string keys and string values. The `country` value is assigned to what's fetched by the map and `ok` indicates if the key is contained in the map or not. In this example, `ok` is assigned to `true` because `"61"` is included in the map.
What does the following code print? countryCodes := map[string]string{ "93": "Afghanistan", "374": "Armenia", "61": "Australia", } country, ok := countryCodes["999"] fmt.Println(country == "", ok == false)	`true true` is printed. The `country` variable is assigned to the zero value of the string type because the `"999"` key isn't included in the map. The `ok` variable is assigned to false because the `"999"` key isn't included in the map.
What does the following code print? countryCodes := map[string]string{ "93": "Afghanistan", "374": "Armenia", "61": "Australia", } if country, ok := countryCodes["93"]; ok { fmt.Println(country, "is a beautiful place") } else { fmt.Println("I don't know that country") }	`Afghanistan is a beautiful place` is printed. The `ok` variable is assigned to `true` because the `"93"` key is included in the map.
What does the following code print? countryCodes := map[string]string{ "93": "Afghanistan", "374": "Armenia", "61": "Australia", } if country, ok := countryCodes["111"]; ok { fmt.Println(country, "is a beautiful place") } else { fmt.Println("I don't know that country") }	`I don't know that country` is printed. The `countryCodes` map doesn't have a value associated with the `"111"` key, so `ok` is assigned to false and the `else` condition is evaluated.
What does the following code print? meaning := map[string]map[string]string{ "red": map[string]string{ "element": "fire", "feeling": "hot", }, "blue": map[string]string{ "element": "water", "feeling": "cold", }, } fmt.Println(meaning["blue"]["feeling"])	`"cold"` is printed. The `meaning` map has string keys and values that are another map. This is an example of a nested map.