External Types

EXTERN_TYPE declares a nominal type supplied by an external runtime. Quxlang knows the type's external identity but does not define its object layout.

Declaration syntax

::java_object INCLUDE_IF(ARCH_IS_JVM)
  EXTERN_TYPE["java.base":"java/lang/Object"];

::java_point INCLUDE_IF(ARCH_IS_JVM)
  EXTERN_TYPE["java.desktop":"java/awt/Point"];

The grammar is:

EXTERN_TYPE["external scope":"external type name"];

Both external names are string literals. The Quxlang declaration name remains the name used in Quxlang type expressions. The terminating semicolon is required.

Because the type belongs to a particular runtime or ABI, its declaration should normally carry an INCLUDE_IF predicate that excludes it from incompatible targets.

GC pointers

On supported managed-runtime targets, ~>T is a GC pointer to an external type:

VAR object ~>java_object;
ASSERT((object??) == FALSE);

The default GC pointer is null. value?? tests for an object and value!? tests for null.

Checked conversions

AS CHECKED ~>Target requests a GC pointer conversion with runtime type validation:

VAR object ~>java_object := stream AS CHECKED ~>java_object;
VAR checked_stream ~>java_print_stream :=
  object AS CHECKED ~>java_print_stream;

The target must support the external type relationship and checked-cast operation. A failed checked conversion follows the managed backend's checked cast failure semantics.

Layout boundary

An external type is opaque to Quxlang layout computation. It is not a Quxlang STRUCT, and declaring it does not provide fields, constructors, or member functions. Operations on its values are supplied through GC pointer operations and External Procedures.

See Target Availability and Backends and Layout.