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digitalmars.D.learn - Create D binding for C struct containing templated class

reply Andre Pany <andre s-e-a-p.de> writes:
Hi,

I try to write a binding for the GRPC core. There is a struct 
which has some ugly fields:
(https://github.com/grpc/grpc/blob/master/src/core/lib/surface/call.cc#L229)

struct grpc_call {
   gpr_refcount ext_ref;
   gpr_arena* arena;
   ...
   grpc_core::ManualConstructor<grpc_core::SliceBufferByteStream> 
sending_stream;
   grpc_core::OrphanablePtr<grpc_core::ByteStream> 
receiving_stream;


ManualConstructor is defined as:
https://github.com/grpc/grpc/blob/50cecca24d4826dea4595b514a332fca5783074b/src/core/lib/gprpp/manual_constructor.h#L168

template <typename Type>
class ManualConstructor {
  public:
   Type* get() { return reinterpret_cast<Type*>(&space_); }
   const Type* get() const { return reinterpret_cast<const 
Type*>(&space_); }


My C / C++ knowledge is very limited and I also do not know how 
much D matured regarding C / C++ integration. Is it possible to 
write a binding in D for these constructs or isn't it supported 
by D?

Kind regards
André
Jun 28 2018
parent reply evilrat <evilrat666 gmail.com> writes:
On Thursday, 28 June 2018 at 18:43:11 UTC, Andre Pany wrote:
 Hi,

 I try to write a binding for the GRPC core. There is a struct 
 which has some ugly fields:
 (https://github.com/grpc/grpc/blob/master/src/core/lib/surface/call.cc#L229)

 struct grpc_call {
   gpr_refcount ext_ref;
   gpr_arena* arena;
   ...
   
 grpc_core::ManualConstructor<grpc_core::SliceBufferByteStream> 
 sending_stream;
   grpc_core::OrphanablePtr<grpc_core::ByteStream> 
 receiving_stream;


 ManualConstructor is defined as:
 https://github.com/grpc/grpc/blob/50cecca24d4826dea4595b514a332fca5783074b/src/core/lib/gprpp/manual_constructor.h#L168

 template <typename Type>
 class ManualConstructor {
  public:
   Type* get() { return reinterpret_cast<Type*>(&space_); }
   const Type* get() const { return reinterpret_cast<const 
 Type*>(&space_); }


 My C / C++ knowledge is very limited and I also do not know how 
 much D matured regarding C / C++ integration. Is it possible to 
 write a binding in D for these constructs or isn't it supported 
 by D?

 Kind regards
 André
No, unfortunately D cannot interface with C templates, only C++ templates. But just by coincidence this is C++ source code (and so the templates). So it is possible but there is few catches. - template functions/methods could be inlined by compiler, which means you may (or may not) have to implement it in D (either copy-paste and adapt, or make own ABI compatible implementation) - most of the methods in this particular template is purely C++ specific convenience helpers, all of this isn't strictly needed in D, just for example operator-> could simply be replaced with alias this. - the only data member in this template is the std::aligned_storage, which you can probably ignore completely and instead just use fixed-size ubyte[] array with align, again just make struct with alias this and align its content same way as aligned_storage does. And much more-more other things to keep in mind. But the most important thing, are you absolutely sure this is a part of the public API and not the implementation specific internals? Because normally you don't #include anything other than .h* files, this is a source file, and it is not even sits in the include folder.
Jun 28 2018
parent reply Andre Pany <andre s-e-a-p.de> writes:
On Friday, 29 June 2018 at 01:38:23 UTC, evilrat wrote:
 On Thursday, 28 June 2018 at 18:43:11 UTC, Andre Pany wrote:
 [...]
No, unfortunately D cannot interface with C templates, only C++ templates. But just by coincidence this is C++ source code (and so the templates). So it is possible but there is few catches. - template functions/methods could be inlined by compiler, which means you may (or may not) have to implement it in D (either copy-paste and adapt, or make own ABI compatible implementation) - most of the methods in this particular template is purely C++ specific convenience helpers, all of this isn't strictly needed in D, just for example operator-> could simply be replaced with alias this. - the only data member in this template is the std::aligned_storage, which you can probably ignore completely and instead just use fixed-size ubyte[] array with align, again just make struct with alias this and align its content same way as aligned_storage does. And much more-more other things to keep in mind. But the most important thing, are you absolutely sure this is a part of the public API and not the implementation specific internals? Because normally you don't #include anything other than .h* files, this is a source file, and it is not even sits in the include folder.
Thanks a lot for the great help. You are right, until now I haven't looked at the include folder, I thought the "surface" folder is the folder with the public api. But it seems also in the include folder, the header files contains references to the grpc_call struct. https://github.com/grpc/grpc/blob/master/include/grpc/impl/codegen/grpc_types.h#L70 Kind regards André
Jun 28 2018
parent evilrat <evilrat666 gmail.com> writes:
On Friday, 29 June 2018 at 06:04:10 UTC, Andre Pany wrote:
 Thanks a lot for the great help.
 You are right, until now I haven't looked at the include 
 folder, I thought the "surface" folder is the folder with the 
 public api. But it seems also in the include folder, the header 
 files contains references to the grpc_call struct.
 https://github.com/grpc/grpc/blob/master/include/grpc/impl/codegen/grpc_types.h#L70
It just declares new type(like forward declaration), so you should be able to do the same thing, or declare the actual struct with no members: struct grpc_call{}
Jun 28 2018