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Object Types

Reference types are either object reference types or function reference types. Additionally, the special any reference type may refer to an object or function of any type.

object_type
    : identifier
    | "Type"
    | "Metatype"
    | "Any"
    ;

Ordinary Object Types

An ordinary object type is a reference to an object. This object could be of a concrete class type or a trait type.

Type and Metatype

The type "Type" is the type of all objects that represent types during reflection and in generics. The default type of a generic parameter is "Type" (thus "class Foo[T]" and "class Foo[T: Type] are equivalent). Any generic parameter with this type is referred to as a "type parameter". Note that "Type" is a reference type. This was necessary to allow metatypes to be subtypes of it.

Objects representing the type of classes and structs have a type that is a subtype of "Type". When calling associated functions as "Example.function()", the expression "Example" has a type that is a subtype of "Type". Metatypes describe the associated functions and initializers on the type object. The meta type of a type can be accessed using the "type" property, for example "Example.type".

These types can be very confusing. For some, an example clarifies the relationship.

let example: Example = Example();
let metatype: Example.type = Example;
let type: Type = metatype; // Example.type <: Type

Any Type

All object and function types are a subtype of the "Any" type. The Any type is a trait that defines the published sealed fn identity_hash(id self) -> nuint where Self: class | struct method.