RAII.nim

{.experimental.}

type Refcounted = ref object
    rc: int
    value: int

type A = object
    r: Refcounted

proc newA(value: int): A =
    result.r = Refcounted(value: value)

proc `=destroy`(a: A) =
    echo "destroy ", (if a.r.isNil: "nil" else: $(a.r))
    if not a.r.isNil:
        dec a.r.rc
        if a.r.rc == 0:
            echo "destroy: ", a.r.value

proc `=`(lhs: var A, rhs: A) =
    echo "assign from ", (if rhs.r.isNil: "nil" else: $(rhs.r)) , " to ", (if lhs.r.isNil: "nil" else: $(lhs.r))
    if lhs.r != rhs.r:
        `=destroy`(lhs)
        lhs.r = rhs.r
        if not lhs.r.isNil:
            inc lhs.r.rc

proc testA(a: A) =
    echo "testA 1"
    var b = a
    echo "testA 2"

block:
    var v: A

    block:
        var v1 = newA(1)
        var v2 = v1
        testA(v2)
        var v3 = v2
        echo "Exiting scope 1"
        v = v1
    echo "Exiting scope 2"