Dictionaries in Mojo

Key-value storage with a declared key type and value type.

def main() raises:
    var stock = Dict[String, Int]()
    stock["apples"] = 12
    stock["pears"] = 4
    # Reading a key can fail, so main is marked raises.
    stock["apples"] += 3
    print(len(stock), stock["apples"])
    print("pears" in stock, "figs" in stock)

How it works

Dict[String, Int]() creates an empty map.
Assignment adds or replaces a key, and += reads then writes.
Reading a key can fail, so main carries raises; in cannot fail.

Keywords and builtins used here

Int
String
def
len
main
print
var

The run, in numbers

Lines: 8
Characters to type: 239
Tokens: 66
Three-star pace: 85 tpm

At the three-star pace of 85 tokens a minute, this run takes about 47 seconds.

Type this snippet

Step 3 of 6 in Collections, step 14 of 26 in Language basics.

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