types.md

Types

There are three main categories of types in Adamant: empty types, value types and reference types. In addition to those, there are a number of other categories of types that are special in some way.

The empty types are those types for which there is no value of that type. Both value and reference types may be generic types, which take generic parameters. Generic parameters can be types (both value and reference types) or constant values. Generic parameters that are types are called type parameters and can be used as types. Optional types modify value types or reference types to add a none value. Variable reference types aka ref types are a special form of reference with their own rules. Additionally, type expressions allow the construction of new types by intersecting and unioning existing types within certain limitations.

type
    : empty_type
    | value_type
    | reference_type
    | type_parameter
    | optional_type
    | variable_reference_type
    | type_expression
    ;

The values types can be further divided into a number of subcategories. Most value types are struct types. The simple types are predefined value types identified with keywords. The tuple type is a predefined type for tuples values. Class value types are value types for each of the non-trait object types. Pointer types allow unsafe code to directly use pointers to addresses in memory.

value_type
    : struct_type
    | simple_type
    | tuple_type
    | class_value_type
    | pointer_type
    ;

Note that while value types are declared to be subtypes of reference types, the reality is more complicated. Given value type S that is a subtype of reference type T, then ref S <: T. There is also an implicit boxing conversion from S to T$owned which consumes the value (i.e. the value is moved into the box).