type-aliases-const.md

Type aliases and const values

Type aliases

using declares a transparent alias for an existing Absolute type:

using Count = int32;
using IntBox = Box<int32>;
using Buffer = int32[];

Aliases may be declared at module or namespace scope. Their target may be a primitive, enum, struct, class, concrete generic specialization, array, task, or raw/managed pointer type. Alias declarations are order-independent and may refer to another alias. Cycles, duplicate names, and unknown targets are semantic errors. Generic alias parameters are not supported yet; alias a concrete generic specialization instead.

Aliases do not create a distinct runtime type or LLVM layout. Overload resolution, generic inference, ABI checks, and code generation use the fully resolved underlying type.

Const values

Variables, fields, and parameters use a prefix const:

const int32 answer = 42;

int32 add(const int32 left, int32 right) {
    return left + right;
}

A local or global const variable requires an initializer. A const field may be initialized by its containing constructor, but cannot be assigned afterward. The analyzer rejects direct and compound assignment, increment/decrement, deletion, and taking a mutable raw address from a const value. Array elements and fields of a const value object are also immutable.

Const is shallow for pointer bindings: const T* value prevents replacing or deleting the pointer variable, but does not make the pointed-to T const. Pointee constness will be a separate type-system feature if needed.

Methods place const after the parameter list:

int32 read() const {
    return value;
}

A const method cannot mutate fields or invoke a non-const method. Interface implementations must match the const contract of the declared method.