Maps
8 min · Scala
Store values under named keys instead of numbered positions.
Enemy 1 of 5
Creating and reading a Map
A Map lets you look up a value by a name, called a key, instead of by position. Use it when data has natural labels, like a player's stats.
This code builds a Map with a name and a score, then prints the value stored under the key name. Press Run to see it.
Why this works
A `List` is great when order matters and you look things up by position, but plenty of real data is more naturally described by a name than a slot number: a player's stats, a word's dictionary definition, a config setting. A `Map` associates each key with a value and lets you look values up by that key directly, without needing to remember which position they happen to sit at.
`Map("key" -> value, ...)` builds an immutable map from a series of key-value pairs, each written with the `->` arrow. Reading a value back out uses function-call syntax with the key: `player("name")`. Like `List`, Scala's default `Map` is immutable, nothing about it changes after creation.
Looking up a key that doesn't exist throws a runtime exception, the same way an out-of-range list index does. If a key might be missing, Scala's `Map` also has a `.get("key")` method that returns an `Option` (either `Some(value)` or `None`) instead of throwing, which is the safer choice once you're past these very first examples.
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