# Containers

Type Declaration,
example
Description
List List<Type>,
List<Int32>
A variable-length sequence consisting of same-type elements.
Dictionary Dict<KeyType, ValueType>,
Dict<String,Int32>
Set of key-value pairs with a fixed type of keys and values.
Set Set<KeyType>,
Set<String>
A set of elements with a fixed type is a special case of a dictionary with the Void value type.
Tuple Tuple<Type1, ..., TypeN>,
Tuple<Int32,Double>
Set of unnamed fixed-length elements with types specified for all elements.
Structure Struct<Name1:Type1, ..., NameN:TypeN>,
Struct<Name:String,Age:Int32>
A set of named fields with specified value types, fixed at query start (must be data-independent).
Stream Stream<Type>,
Stream<Int32>
Single-pass iterator by same-type values, not serializable
Variant on tuple Variant<Type1, Type2>,
Variant<Int32,String>
A tuple known to have exactly one element filled
Variant on structure Variant<Name1:Type1, Name2:Type2>,
Variant<value:Int32,error:String>
A structure known to have exactly one element filled
Enumeration Enum<Name1, Name2>,
Enum<value,error>
A container with exactly one enumeration element selected and defined only by its name.

If needed, you can nest containers into each other in arbitrary combinations, for example: List<TupleInt32,Int32>.

In certain contexts, optional values can also be considered a container type (Optional<Type>) that behaves as a list of length 0 or 1.

To create literals of list containers, dictionary containers, set containers, tuple containers, or structure containers, you can use the operator notation.
To create a variant literal over a tuple or structure, use the function Variant.
To create an enumeration literal, use the function Enum.

To access container elements, use a dot or square brackets, depending on the container type.