[Boost-users] Boost version of Loki StaticDispatcher

Subject: [Boost-users] Boost version of Loki StaticDispatcher
From: Glenn Macgregor (gmacgregor_at_[hidden])
Date: 2009-12-15 13:21:12

Hi All,

I am looking to replace Loki with Boost since we use Boost for other parts of projects. Example of current situation:

template<typename T>
struct param_traits {};

template<>
struct param_traits<long> {
                typedef long param_type;

static param_type init() { return 0; }
static bool fromString(const string &str, param_type &value, int base) {
                // Do conversion
}

static string toString(param_type &value, const string &fmt) {
                // Do conversion
}
};

template<>
struct param_traits<double> {
                typedef double param_type;

static param_type init() { return 0.0; }
static bool fromString(const string &str, param_type &value, int base) {
                // Do conversion
}

static string toString(param_type &value, const string &fmt) {
                // Do conversion
}
};

Class BaseParamValue {
public:
                virtual ~BaseParamValue() {};
                virtual bool fromString(const string &str, int base = 0) = 0;
                virtual string toString(const string &ftm = "") = 0;

                static BaseParamValue *create(const string &type) {
                                if (type == string("LONG")) {
                                                return new ParamValue<long>();
                                } else if (type == string("DOUBLE")) {
                                                return new ParamValue<double>();
                                }

                                return 0;
                }
};

template<typename T>
class ParamValue : public BaseParamValue {
public:
                typedef param_traits<T> traits_type;
                typedef typename traits_type::param_type ParamType;

                ParamValue() :
                                mValue()
                {
                }

~ParamValue() {};

bool fromString(const string &str, int base) {
                return traits_type::fromString(str, mValue, base);
}

string toString(const string &fmt) {
                return traits_type::toString(mValue, fmt);
}

private:
                ParamType mValue;
};

class Param {
public:
                Param() :
                                mParamValue(0)
                {
                }

                Param(const string &type) :
                                mParamValue(BaseParamValue::create(type))
                {
}

~Param() {
                delete mParamValue;
}

private:
                BaseParamValue *mParamValue;
};

So as you can see I store a BaseParamValue in the param class instead of making the Param class itself a template, which is not an option at the moment. I am currently using loki StaticDispatcher to up cast (I guess) to the correct templatized instance in the operations. What I am trying to get done is the following:

class TestVisit {
public:
                TestVisit();
                ~TestVisit();

                void visit(const ParamValue<long> &value);
void visit(const ParamValue<double> &value);
};

Is there a way in Boost to go from a BaseParamValue * to the actual templatized ParamValue and call the correct visit using: testVisit.visit(*mParamValue). Currently I get a compiler error saying: cannot conver parameter 1 from 'BaseParamValue' to 'const ParamValue<T> &'

Sorry for the long post, thanks in advance.

 Glenn