I was trying to read DIP1000, and I've made about half way through it. I found it confusing/hard to follow, and sometimes inconsistent. So I want to ask for some clarification. Help would be appreciated.

> # Abstract
> A garbage collected language is inherently memory safe.

I think in order for this sentence to make sense, we need to define what is a "garbage collected language". Does any language that supports GC count? Because there's Boehm GC for C. Does D count? Because dmd has this compiler switch: -boundscheck=off, which clearly makes the language not memory safe.

> [...]
> # Description
> ## Definitions
> We also define lifetime for each value, which is the extent during which a value can be safely used.

OK.

> * For an unrestricted pointer, [...] lifetime is dictated by the lifetime of the data to which the pointer points to.

Why? The pointer itself can be used safely in its lexical scope just like a value type. It's *pointer which has the lifetime of the data. Maybe 'using' a pointer means dereferencing it?

> [...]
> ### Algebra of Lifetimes
> expression	lifetime	notes
> *e		∞		Lifetime is not transitive

Huh? I guess this is true if *e is a value type, since then it would be copied. But what about:

int a;
int *b = &a;
int **c = &b;

*c = b so lifetime(*c) = lifetime(b), right? And then as per the example given

> if (...) {
>    int x;
>    p = &x; // lifetime(p) is now equal to lifetime(x)
> }

lifetime(b) = lifetime(a). So lifetime(*c) = lifetime(a) != ∞.

Maybe that example is poorly written? Because:

> ## Fundamentals of scope
> [...]
>     scope int* a = &global_var; // OK per rule 1, lifetime(&global_var) > lifetime(a)
>     a = &global_var;       // OK per rule 1, lifetime(&global_var) > lifetime(a)

As per the previous example. lifetime(a) will become lifetime(&global_var) after first assignment. Would it be better if we say lifetime(&global_var) > reachability(a)?

BTW, reachability() is defined at the beginning of this DIP, but never used afterwards. Why bother defining it?