Maps

A List is great when order matters and you look things up by position. Often, though, you want to look something up by a meaningful name instead: a player's username, a product's SKU, a word you're tallying. That's what a Map is for: it stores key-value pairs and lets you retrieve a value quickly given its key, regardless of how many pairs it holds.

You build one with mapOf("key" to value, ...): the to keyword is Kotlin's readable way of pairing a key with a value (it's actually a small infix function under the hood, not special syntax baked into the language, but you don't need to worry about that detail yet). Once you have a map, you read a value the same way you'd index into a list, but with a key instead of a position: scores["Ada"].

mapOf() creates a read-only map: you can look things up but not add or change entries after creation, matching the listOf() versus mutableListOf() distinction from the Lists lesson.