On 7/13/16 5:19 AM, John Colvin wrote:
"Casting away immutable is undefined behaviour": the following code has
undefined results (note, not implementation defined, not
if-you-know-what-you're-doing defined, undefined), despite not doing
anything much:
void foo()
{
immutable a = new int;
auto b = cast(int*)a;
}
"modifying immutable data is undefined": The above code is fine, but the
following is still undefined:
void foo()
{
immutable a = new int;
auto b = cast(int*)a;
b = 3;
}
Interesting distinction. We must render the latter undefined but not the
former. Consider:
struct S { immutable int a; int b; }
S s;
immutable int* p = &s.a;
It may be the case that you need to get to s.b (and change it) when all
you have is p, which is a pointer to s.a. This is essentially what makes
AffixAllocator work.
Andrei
