Aliases

An alias declaration gives a new name to an existing type surface. The alias does not create a new object model. It gives the type a stable name that can be reused in declarations, signatures, and receiver-qualified routines.

There are two related forms:

• aliasing
• extending

Aliasing

typ[ali] I5: arr[int, 5];

Now code can use I5 instead of repeating arr[int, 5]:

var fiveIntegers: I5 = { 0, 1, 2, 3, 4 };

Another example is naming a constrained color component type:

typ[ali] rgb: int[8][.range(255)];
typ[ali] rgbSet: set[rgb, rgb, rgb];

Aliases are useful because:

• they avoid repeating long type expressions
• they give a type surface a meaningful name
• they provide a named receiver surface for receiver-qualified routines

Receiver-qualified routines remain procedural. If a value is written as value.method(arg), read that as call-site sugar for method(value, arg). The routine is still separate from the data declaration.

Standalone alias declarations

The standalone ali declaration is the short form of the same aliasing surface:

ali Meters: int;

Like other declarations, an alias is package-visible by default. Exporting it across package boundaries uses the same option surface as typ, fun, and var:

ali[exp] Meters: int;

exp is the only option an alias declaration accepts.

Current milestone note:

• aliasing and extension over current V1 built-in and declared types are part of the present language surface
• true foreign-type interop remains later work
• C ABI and Rust interop belong to the planned V4 milestone, not the current compiler contract

Extending

Extensions expose an existing type under an explicit receiver surface so that new receiver-qualified routines can be declared for it.

typ[ext] type: type;

This is still procedural. It does not turn the type into an object or create inheritance. It only allows routines to be written against that receiver surface.

For example, an explicit receiver surface for int:

typ[ext] int: int;

pro (int)print(): non = {
    .echo(self)
}

pro main(): non = {
    5.print()
}

The call 5.print() is still just receiver sugar for print(5).

An older version of this chapter used a string-to-vector extension containing yield. That mixed future generator design into the current alias contract. Language yield is parsed and retained for future work, but the current typechecker and lowerer reject it; it is not part of V3. Alias and extension support therefore does not imply generator support.