On Wed, 04 Mar 2009 19:39:06 +0300, Don <nos...@nospam.com> wrote:
Andrei Alexandrescu wrote:
Don wrote:
Andrei Alexandrescu wrote:
And there is no reference type with two subtypes. It's one type in
the language and one in the library. Maybe-null (the library) is a
supertype of non-null (the default).
One problem I can see is with extern(C),(Windows) functions, since
pointers are maybe-null in C. The name-mangling has to work out.
I can't see how this can be done without the compiler knowing
SOMETHING about both nullable and non-nullable types.
At the bare minimum, you need to deal with maybe-null returns and
reference parameters from C functions.
Walter is thinking of making only references non-null and leaving
pointers as they are. (I know, cry of horror.) But say pointers are
also non-null. Then:
extern(C) MaybeNull!(void*) malloc(size_t s);
will work, provided that MaybeNull has no size overhead and that
word-sized structs are returned in the same register as word returns (I
seem to remember Walter told me that's the case already).
Here's a typical annoying Windows API function
--------
int GetTextCharsetInfo(
HDC hdc, // handle to DC
LPFONTSIGNATURE lpSig, // data buffer
DWORD dwFlags // reserved; must be zero
);
lpSig
[out] Pointer to a FONTSIGNATURE data structure that receives
font-signature information. The lpSig parameter can be NULL if you do
not need the FONTSIGNATURE information.
---------
How do you do this?
Don.
extern(System) int GetTextCharsetInfo(
HDC hdc,
MaybeNull!(FONTSIGNATURE*) lpSig, // or whatever
DWORD dwFlags);
GetTextCharsetInfo(hdc, null, flags); // fine
GetTextCharsetInfo(hdc, &sig, flags); // also ok
