Generics
Helios supports generic type parameters for functions, structs, and enums. The syntax for generics is similar to lists, Map and Option.
Generic functions
Example:
func deserialize[A](a: Data) -> A {
A::from_data(a)
}
When calling a function, the type parameters are infered wherever possible. In this example however A can't be inferred and must be specified before calling the function:
my_bool: Bool = deserialze[Bool](my_bool_data); ...
The type parameter can optionally be constrained with a typeclass, for example with the builtin Valuable typeclass:
func get_value[V: Valuable](v: V) -> Value {
v.value
}
Generic structs and enums
User types like structs and enums can also have generic type parameters. For example:
struct Pair[A, B] {
a: A
b: B
}
When instantiating such a generic type, type inference isn't available, and the field types must be specified explicitly:
my_pair = Pair[Int, Int]{1, 2}; ...
An example of a generic enum:
enum BinaryTree[A] {
Leaf { value: A }
Node {
value: A
left: BinaryTree[A]
right: BinaryTree[A]
}
}
Similar to generic functions, the type parameters of generic structs and enums can be constrained using typeclasses.
Note: all type parameters must be used in the fields of the struct or enum, not just in the methods.
Note: generic structs and enums can contain generic methods with additional type parameters.
Type classes
Typeclasses are used to constrain a type parameter of a generic function or user-type.
User-defined typeclasses aren't yet possible, there are however three builtin typeclasses: