Aggregate Parameters and Results

Copying a large record or array merely to call a routine would waste time and storage. Nucleus passes aggregates as fixed typed aliases to existing objects.

sub copyPair(source as Pair, destination as Pair)
    destination = source
end

Both parameters refer to caller-owned Pair objects. Assignment copies the complete value into the object bound to destination; it does not make the parameter refer somewhere else. A field write through a parameter is likewise visible to the caller.

Concrete aggregate parameters require exact type identity. Open views from Chapter 9 are the deliberate exceptions for arrays of varying lengths and strings of varying capacities.

Aggregate results are aliases

A routine may return an aggregate type:

sub selected(useFirst as boolean) as Pair
    if useFirst
        return first
    end
    return second
end

The result is not a new temporary Pair. It is a transient alias to existing program-lifetime storage. The caller must consume it immediately: pass it to a compatible parameter, select a field or element, return it again, discard it or copy it through aggregate assignment.

This model avoids heap allocation and prevents an alias carrier from outliving its containing operation. To retain the value rather than the identity, copy it into caller-owned storage:

copyPair(selected(true), second)

Nucleus has no aggregate locals. A routine needing scratch storage receives a caller-provided destination or uses a program object. This is explicit, fixed storage rather than an activation-sized array hidden on the stack.

The companion returns an alias to first, copies its value into second and leaves observed equal to 34.

record Pair
    left as u8
    right as u8
end

var first as Pair = (3, 4)
var second as Pair
var observed as u16 = 0

sub selected(useFirst as boolean) as Pair
    if useFirst
        return first
    end
    return second
end

sub copyPair(source as Pair, destination as Pair)
    destination = source
end

sub main()
    copyPair(selected(true), second)
    observed = u16(second.left) * 10 + u16(second.right)
end

Summary

• Aggregate parameters alias complete caller-owned objects.
• Mutation through a parameter changes the caller's object.
• Concrete aggregate parameters require exact type identity.
• Aggregate results are transient aliases, not copied temporaries.
• Caller-owned storage retains a returned value through explicit assignment.

See storage and lifetime and routine results. The checked companion is 11-aggregate-results.nu.