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[Feat] Expose any tuple from cache C impl #32

Description

@haochengxia
  • Expose one function inner cache impl, dump to export tuples from C to Python, current design is:
    // C code
    typedef struct {
       ValueType type;
       union {
           int i;
           double d;
           const char* s;
           void* ptr;
       } data;
    } AnyValue;
    
    typedef struct {
       AnyValue* items;
       size_t size;
    } C_Tuple_Like;
    
    C_Tuple_Like* make_sample_tuple() {
       C_Tuple_Like* tuple = malloc(sizeof(C_Tuple_Like));
       tuple->size = 3;
       tuple->items = malloc(sizeof(AnyValue) * 3);
       tuple->items[0] = (AnyValue){ .type = TYPE_INT, .data.i = 42 };
       tuple->items[1] = (AnyValue){ .type = TYPE_DOUBLE, .data.d = 3.14 };
       tuple->items[2] = (AnyValue){ .type = TYPE_STRING, .data.s = strdup("hello") };
       return tuple;
    }
    
    // C++ code
    std::tuple<int, double, std::string> convert(const C_Tuple_Like* ctuple);
    
    std::tuple<int, double, std::string> convert_to_tuple(const C_Tuple_Like* input) {
       int i = input->items[0].data.i;
       double d = input->items[1].data.d;
       std::string s = input->items[2].data.s;
       return std::make_tuple(i, d, s);
    }
    
    // To Python
    py::tuple convert_to_py_tuple(const C_Tuple_Like* input) {
       py::tuple result(input->size);
       for (size_t i = 0; i < input->size; ++i) {
           const auto& item = input->items[i];
           switch (item.type) {
               case TYPE_INT:
                   result[i] = py::int_(item.data.i);
                   break;
               case TYPE_DOUBLE:
                   result[i] = py::float_(item.data.d);
                   break;
               case TYPE_STRING:
                   result[i] = py::str(item.data.s);
                   break;
               default:
                   result[i] = py::none();  // fallback
           }
       }
       return result;
    }
    
    m.def("get_tuple", []() {
       C_Tuple_Like* c_tuple = make_sample_tuple();
       auto py_tuple = convert_to_py_tuple(c_tuple);
       // free if needed
       return py_tuple;
    });

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