Basic Borrows

The two borrow operators are $$i (immutable) and $$m (mutable). They introduce a loan on a host variable that lasts as long as the borrowing binding is in scope.

The two operators

int32:value = 42;
$$i int32:r = value;   // immutable borrow — read-only view of `value`
$$m int32:m = value;   // mutable borrow   — read/write alias of `value`

$$i is read-only; $$m allows assignment through the alias and the host sees the write after the loan ends.

The 1-mut XOR N-immut rule

At any point a host can have either:

any number of $$i loans, or
exactly one $$m loan.

Mixing the two on the same host fails:

$$i int32:r = a;
$$m int32:m = a;       // ARIA-023: conflicting borrow on `a`

Two $$m loans on the same host also fail (ARIA-023).

Release

A loan is released when its binding leaves scope. The host is then free to be borrowed again or assigned to:

int32:a = 10;
{
    $$i int32:r = a;   // loan exists inside this block
}                      // loan released here
$$m int32:m = a;       // OK — new loan, no conflict
m = 12;
exit m;                // 12

This pattern is called scope release. The K test 056 locks it in.

`failsafe` and borrow failures

When the borrow checker rejects code at compile time you get an ARIA-023 or ARIA-026 diagnostic and no binary is produced. There is no runtime borrow check — by the time failsafe runs, the rules above are already satisfied. failsafe exists for other runtime faults (panics, OOM, explicit fail).

What "host" means

The host is the variable or path the loan tracks. For

$$m int32:rx = box.leaf.x;