Dictionaries🔗

Dictionaries (dicts) are key-value stores. Keys are always strings; values can be any type.

Creating dictionaries🔗

let person = {"name": "Alice", "age": 30, "active": true}
let empty = {}

Accessing values🔗

Use bracket notation with a string key:

let name = person["name"]     // "Alice"
let age = person["age"]       // 30

Accessing a missing key returns none (no error):

let email = person["email"]
print(email)    // none

if email.is_none() { print("no email on file") }

Two caveats:

• A key whose value is explicitly none is present — d.has(k) returns true for it, even though d[k] and d["absent_key"] are both none. Use d.has(k) when you need to distinguish “unset” from “set to none”.
• If you want a read to fail on a missing key, check d.has(key) first and raise explicitly — d[key] itself always succeeds.

Modifying values🔗

person["age"] = 31             // update existing key
person["email"] = "[email protected]"   // add new entry
let removed = person.remove("email")   // delete a key, returning its value

remove returns none when the key is absent. Together with clear, it mutates its receiver with the same write-back rules as the mutating array methods: mutable places rooted in a let binding write back atomically (including nested places like state["session"].remove("token")), constants are rejected, and a genuine temporary is mutated and then discarded. Because they are mutating methods, they also work through ref parameters and ref self — fn wipe(ref d) { d.clear() } empties the caller’s dict, where d = {} would only rebind the callee’s local.

Methods🔗

Plus the universal d.type(), d.to_str(), d.inspect().

Practical examples🔗

Counting occurrences🔗

let words = ["apple", "banana", "apple", "cherry", "banana", "apple"]
let counts = {}
for word in words {
  if counts.has(word) {
    counts[word] += 1
  } else {
    counts[word] = 1
  }
}

for key in counts {
  print(key + ": " + counts[key].to_str())
}

Storing structured data🔗

let point = {"x": 10, "y": 20}
let x = point["x"].to_str()
let y = point["y"].to_str()
print("Position: ({x}, {y})")

Iterating over entries🔗

let config = {"width": 800, "height": 600, "title": "My App"}
for key in config {
  let val = config[key].to_str()
  print(key + ": " + val)
}

Checking for a key before using it🔗

let settings = {"volume": 80}

if settings.has("volume") {
  let v = settings["volume"].to_str()
  print("Volume is {v}")
} else {
  print("Using default volume")
}