Collections

Arrays

Arrays are defined like so:

[123, 444, 901]

Every element of an array must have the same type, but this type can be a union type, i.e. a combination of multiple types (e.g. a number or a string). Despite this, you should try and ensure an array contains values of the same type.

Tuples

Defined like so:

{"A String", 123, :symbol}

A tuple is a fixed length list of items that can have different types.

We can pass the individual members of a tuple as arguments by placing the * symbol in front of it:

coordinates = {6, 4}
plot(*coordinates)

Named Tuples

Defined like so:

{string: "A String", number: 123, symbol: :symbol}

Named tuples allow us to associate a symbol with each tuple element.

Indexing

Crystal allows random access of tuples and arrays, as opposed to linked-list style behaviour. Crystal will throw an out-of-bounds exception if the index doesn't exist, but you can default the value to nil instead by including ? like so:

list[4]?

Hashes

Defined like so:

{"Key" => :value, "String" => :symbol}

The keys must be of the same type, as do the values. However, like with arrays, these types can be union types, but this should be avoided for simplicity's sake.

includes?

Classes which inherit from Enumerable have the include(...) method, which allows you to search for an object inside them.