Call Sites

Borrows cross function boundaries through $$i and $$m parameters. The checker treats each parameter as a separate loan on the caller's argument.

$$i parameters

func:read_pair = int32($$i Pair:p) {
    pass p.a + p.b;
};

func:main = int32() {
    Pair:pair = Pair{a: 10, b: 20};
    int32:r = read_pair(pair);     // implicit $$i pair for the call
    exit r;                        // 30
};

Multiple $$i arguments to the same call on the same host are fine — they all coexist under the N-immut rule.

$$m parameters

func:bump_a = int32($$m Pair:p) {
    p.a = p.a + 1;
    pass p.a;
};

Only one $$m loan per host is allowed, so a call with two $$m parameters must use different hosts (or different paths):

func:swap = int32($$m int32:x, $$m int32:y) {
    int32:t = x; x = y; y = t;
    pass 0;
};

int32:a = 1;
int32:b = 2;
swap(a, b);                  // OK — different hosts
swap(a, a);                  // ARIA-023 — same host twice

$$m writeback

When a $$m parameter is written through, the new value is visible to the caller after the call returns:

func:set42 = int32($$m int32:x) { x = 42; pass 0; };

func:main = int32() {
    int32:v = 0;
    set42(v);
    exit v;                  // 42
};

(K test 063.) Multiple $$m parameters all writeback independently (K tests 101–103.)

Holding a borrow across a call

If you hold a $$i or $$m loan on host and then call a function that also wants $$m host, the call is rejected. Release the outer loan first (scope it, or finish using it) before calling.

Field-path arguments

You can pass a borrow on a path:

$$m int32:r = pair.a;
some_helper(r);              // r is the host now

But you cannot pass a field expression with an explicit borrow operator in the call list — bind the borrow first, then pass the binding.