Transform macro defined function to templated auto function call

manpreet Best Answer 2 years ago

Currently dealing with some legacy code that defines a macro'ed function and uses the macro param to stamp out a C-style cast and a look up table (array) - note they're all just enums

#define DEFINE_ENUM_RW(a)                                           \
BOOL    r##a(CXMLObject* pxml, void* object, S_XML_TAG * item)   \
...
##a *pc = (##a*)ptr;
...
*pc = (##a)nameENid(s, lut##a);

What I would like to do is pass the enum & array as template parameters so I don't have to alter the function signature as follows:

template <typename T, typename U>
bool xmlReadEnum(CXMLObject* pxml, void* object, S_XML_TAG* item)
...
auto pc = reinterpret_cast<T*>ptr;
...
*pc = static_cast<T>nameENid(st, U);

And then use a simpler macro definition to lay out the function declaration:

#define DEFINE_ENUM_RW(a) \
std::function<bool(CXMLObject*, void*, S_XML_TAG*)> r##a = xmlReadEnum<##a, lut##a>;

But this results in a compilation error

no suitable constructor exists to convert from "" to "std::function"

I'm not entirely sure if my approach is feasible here or if there's a simpler approach that would be more appropriate? If it is a reasonable approach I'm not sure what is missing to allow this to compile?