Using a C++ class in a D associative array
kinke
noone at nowhere.com
Tue Aug 21 00:07:40 UTC 2018
On Monday, 20 August 2018 at 22:16:09 UTC, Jacob Carlborg wrote:
> At the third line there's a call from
> object.TypeInfo_Class.getHash. I looked up to see what the
> "getHash" method is doing in druntime [2], the method looks
> like this:
>
> override size_t getHash(scope const void* p) @trusted const
> {
> auto o = *cast(Object*)p;
> return o ? o.toHash() : 0;
> }
I guess the compiler uses the AA key type's TypeInfo, which is
available for extern(C++) classes too. The
TypeInfo_Class.getHash() then uses the dynamic type via virtual
call, (wrongly) assuming it's always a D class. For an
extern(C++) class, it will either call another virtual function
(no inherited virtual functions from Object), what you were
seeing, or attempt to call... something. ;)
> All this just compiled without any error or warnings. No
> runtime exceptions or asserts were triggered. I just got a
> really weird behavior.
This is somewhat special due to the common TypeInfo.getHash()
signature for all kinds of types, and so just taking a hairy
void* pointer to the byte/real/static array/AA/object/… to be
hashed.
Polishing C++ interop with extern(C++) classes (matching
ctors/dtors, mixed class hiearchies, ability to easily
allocate/construct/destruct/free on the other language side etc.)
has started with v2.081 and is still on-going; there are probably
more places in druntime silently assuming a D class.
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