The Silicon framework design is derived from the static metaprogramming paradigm of the IOD framework. The core of this framework relies on the symbol concept: A set of C++ variable bearing the static introspection of the library. With symbols, declaring a staticaly introspectable object (sio) is one C++ statement:
auto o = D(_name = "John", _age = 42);
// o.name == "John"
// o.age == 42
Here, the symbols _name and _age hold the following semantics: The resulting object will have two members o.name and o.age. The first is a string representing "John" and the second is an int representing 42.
_name and _age are plain C++ variables and the previous code will not compile without their definitions:
// Guards avoid multiple definitions of symbols.
#ifndef IOD_SYMBOL_NAME
#define IOD_SYMBOL_NAME
iod_define_symbol(name);
#endif
#ifndef IOD_SYMBOL_AGE
#define IOD_SYMBOL_AGE
iod_define_symbol(age);
#endif
Furthermore, to avoid name conflicts, iod places all the symbols in the namespace s. Then, using namespace s allows to skip the s:: prefix.
The big advantage of SIOs over plain C++ object is their static introspection. The IOD foreach construct allows to apply a function to each member of an object. A member gives access to its associated value and symbol.
For example, one can easily build a basic serializer:
// Define an object
auto o = D(_name = "John", _age = 42, _city = "NYC");
// Output the structure of the object to std::cout:
// name:John
// age:42
// city:NYC
foreach(o) | [] (auto& m) { std::cout << m.symbol().name() << ":"
<< m.value() << std::end; }
Silicon makes heavy use of iod symbols. To automate the declaration of every symbols, IOD provides a symbol definition generator. It looks for variables starting underscore and write their definition in a C++ header:
$ iod_generate_symbols
Usage: iod_generate_symbols input_cpp_file1, ..., input_cpp_fileN, output_cpp_header_file