User talk:Schuetzm/scope2
Example for the inference algorithm
Applied to the function deadalnix used to demonstrate the rvalue/lvalue problem:
(1) foo()
is @safe
, making its param scoped:
void foo(scope int** a) {
// no inference for `a` => self-owned
// ("mystery scope" in your terms)
// => SCOPE(a) := [a] (final)
int** b;
// => SCOPE(b) := [] (incomplete)
b = a;
// scope of `a` is fixed => do nothing
int d;
int* c;
// => SCOPE(c) := [] (incomplete)
c = &d;
*b = c;
// assignment from `c`:
// => SCOPE(c) |= SCOPE(*b) = [] | [static] (final)
// (dereferencing loses information => static)
// ---------------------------------------------------
// we now have:
// SCOPE(a) = [a]
// SCOPE(b) = []
// SCOPE(c) = [static]
// => all resolved
// ---------------------------------------------------
// => satisfiable, now let's check the assignments:
int** b = a; // [] := [a] => OK
int d;
int* c = &d; // [static] := [d] => BAD
*b = c; // [static] := [static] => OK
// => invalid assignment
// note how it even traces where the bad value comes from
}
(2) foo()
is in a template, param scope gets inferred
void foo(T)(T** a) {
// start with empty scope params
// => SCOPE(a) := [] (incomplete)
T** b;
// start with empty scope for locals
// => SCOPE(b) := [] (incomplete)
b = a;
// only access to `a`:
// => SCOPE(a) |= SCOPE(b)
// => DEFER because SCOPE(b) is incomplete
T d;
T* c;
// => SCOPE(c) = [] (incomplete)
c = &d;
*b = c;
// assignment from `c`:
// => SCOPE(c) |= SCOPE(*b) = [] | [static] = [static]
// ---------------------------------------------------
// we now have:
// SCOPE(a) = []
// SCOPE(b) = []
// SCOPE(c) = [static]
// unresolved:
// SCOPE(a) |= SCOPE(b)
// resolve:
// SCOPE(a) := [] | [] = []
// => all resolved
// ---------------------------------------------------
// => satisfiable, now let's check the assignments:
int** b = a; // [] := [] => OK
int d;
int* c = &d; // [static] := [d] => BAD
*b = c; // [static] := [static] => OK
// => invalid assignment
// again, the culprit can be detected
}