Interfacing C functions with safer ptr/length

[Andrei Alexandrescu]

On 10/29/10 21:11 CDT, bearophile wrote:
> I am toying with more ideas to strengthen D type system a bit in few spots. This is a minor thing, I don't know if this is a common enough situation to deserve compiler support, maybe not.
>
> If I want to use a C function from D code, and such C function has as arguments both a pointer that represents an array and int value that represents its length, is it possible to use a compact syntax that tells the compiler how to pack or unpack the contents of the fat D pointer that represents a D array?
>
> Something like this:
>
> extern(C) void foo(int[].ptr, int, int[].length);
>
> If the function needs two or more arrays the compiler asks you to give names to tell apart their parts in the signature:
>
> extern(C) void bar(int[].ptr a1, int[].length a1, int[].ptr a2, int[].length a2);
>
> This is supposed to avoid some bugs in using from D with dynamic arrays those functions foo() and bar().
>
> So you have to call foo() like this:
>
> foo(v.ptr, n, v.length);
>
> While this generates a compile-time error because here the D code calls this function with parts from different arrays:
>
> foo(v1.ptr, n, v2.length);
>
> This too generates compile-time errors because m isn't the length of v1 and p isn't the ptr of v2:
>
> foo(v1.ptr, n, m);
> foo(p, n, v2.length);
>
> (This idea was born from reading about Deputy, a system to build safer Linux drivers.) I am trying to invent ideas better than this one.
>
> Bye,
> bearophile

Other static checkers have that too. They invariably address what Walter 
calls "C's biggest mistake" (and I think he's dead on to that).

In D:

private extern(C)
{
     void foo(int*, int, size_t length);
     void bar(int* a1, size_t a1, int* a2, size_t a2);
}

void foo(int[] a, int b)
{ return foo(a.ptr, b, a.length); }
void bar(int[] a1, int[] a2)
{ return bar(a1.ptr, a1.length, a2.ptr, a2.length); }


Andrei