Conversions

An explicit conversion uses AS, optionally followed by a conversion mode:

VAR wide I64 := 300;
VAR narrowed I8 := wide AS PARTIAL I8;
VAR checked I32 := wide AS CHECKED I32;
VAR assumed I32 := wide AS ASSUME I32;
VAR approximate F32 := 0.4 AS APPROXIMATE F32;

Modes

Form	Contract
expression AS Type	Ordinary explicit conversion with no extra permission
AS EXPLICIT Type	Selects an explicit user conversion category
AS PARTIAL Type	Permits a partial representation result, such as discarded high bits
AS CHECKED Type	Requires validity to be checked and faults on failure
AS ASSUME Type	Makes validity a program precondition
AS APPROXIMATE Type	Permits an inexact numeric result
AS REINTERPRET Type	Selects a representation-level conversion explicitly allowed by the type system
AS UNCHECKED_STATIC_DOWNCAST PointerOrReferenceType	Recovers an exact complete struct type from an unambiguous base; no runtime check
AS DYNAMIC PointerType	Performs a checked polymorphic downcast or cross-cast

Narrowing

Narrowing is not silently accepted. The programmer selects whether truncation, a dynamic check, an assumption, or approximation matches the intended semantics.

Pointer reinterpretation

Current pointer reinterpretation supports explicit paths such as conversion through VOID while preserving pointer category and validity constraints:

VAR pointer CONST->I32 := value<-;
VAR erased CONST->VOID := pointer AS REINTERPRET CONST->VOID;
VAR restored CONST->I32 := erased AS REINTERPRET CONST->I32;

REINTERPRET does not establish an unrelated live type in storage. Typed Storage and Explicit Lifetime specifies lifetime transitions.

User-defined conversions

Constructor parameter names select the corresponding conversion categories, including @OTHER, @EXPLICIT, @PARTIAL, @CHECKED, @ASSUME, @APPROXIMATE, and @REINTERPRET. See Constructors and destructors.

AS DYNAMIC is restricted to polymorphic instance pointers and returns null when no unique target subobject exists. See Inheritance for qualification, RTTI, and target-support rules.

AS UNCHECKED_STATIC_DOWNCAST is a built-in operation for instance pointers and references, including nonpolymorphic structs. It cannot be overloaded. The complete type must exactly match the destination, and repeated nonvirtual source bases cause a compilation error. See Unchecked static downcasts for null handling, qualification, virtual bases, and undefined behavior.