Odin by Example: Maps

Maps store key:value pairs. Keys must be of a comparable type, such as strings or integers.

The zero value of a map is nil. Use make to create a map before adding entries.

Accessing a missing key returns the zero value of the element type. Use the comma-ok idiom or the "in" operator to check whether a key exists.

The built-in delete_key procedure removes a key. The built-in len procedure returns the number of key:value pairs.

$ odin run maps.odin -file
alice: 95
bob: 87
zero value: 0
charlie present: false
alice is in the map
len: 2
len: 1
len: 2

package main

import "core:fmt"

main :: proc() {
	// Create a map with string keys and int values.
	scores := make(map[string]int)

	// Add entries.
	scores["alice"] = 95
	scores["bob"] = 87

	fmt.println("alice:", scores["alice"])
	fmt.println("bob:", scores["bob"])

	// Accessing a missing key returns the zero value.
	fmt.println("zero value:", scores["charlie"])

	// Comma-ok idiom: ok is true if the key exists.
	_, ok := scores["charlie"]
	fmt.println("charlie present:", ok)

	// The "in" operator also checks for key existence.
	if "alice" in scores {
		fmt.println("alice is in the map")
	}

	fmt.println("len:", len(scores))

	// Remove a key.
	delete_key(&scores, "bob")
	fmt.println("len:", len(scores))

	scores["charlie"] = 92
	fmt.println("len:", len(scores))

	// Iterate over keys and values. Order is not
	// specified.
	for key, value in scores {
		fmt.println(key, value)
	}
}

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