Collections and everyday data
Acton has three built-in collection types for everyday data:
- Lists keep values in order and allow duplicates.
- Dictionaries map keys to values.
- Sets keep unique values and make membership checks direct.
If you are unsure where to start, choose by the question you want to answer. Use a list when order matters, a dictionary when you need to look things up by key, and a set when you mainly care about uniqueness or membership.
Use this section when you need to keep many values together and work with them as one logical value.
Collections pair naturally with higher order functions and comprehensions. That is the common Acton path for turning one collection into another without spreading the transformation across several places.
All collection types are statically typed. A list has one element type, a set has one element type, and a dictionary has one key type and one value type.