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typedvalue.h

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//
// typedvalue - type-safe reference transmission of arbitrary types.
//
// This slight-of-hand pair of classes allows arbitrary types to be passed through an API
// without losing C++ type safety. Specifically, the type is encapsulated in C++ polymorphism,
// and can be resolved through the C++ typeinfo/dynamic_cast system in a fairly
// convenient way. This is intended to replace passing (void *) arguments around.
// It is obviously not meant to replace proper class hierarchies in APIs.
//
#ifndef _H_TYPEDVALUE
#define _H_TYPEDVALUE

#include <security_utilities/utilities.h>
#include <security_utilities/debugging.h>


namespace Security {


//
// A GenericValue can represent any (one) type. Note the template assignment
// that works *only* for the type it actually represents. Note particularly that
// no automatic conversions are made (other than to subclass).
//
class GenericValue {
public:
    virtual ~GenericValue();
    
    template <class V>
    void operator = (const V &value);
};


//
// A TypedValue is a particular typed instance of a GenericValue
//
template <class Value>
class TypedValue : public GenericValue {
public:
    TypedValue() : mValue() { }
    TypedValue(const Value &v) : mValue(v) { }
    Value &value()                              { return mValue; }
    operator Value &()                    { return mValue; }
    void operator = (const Value &value) { mValue = value; }
    
private:
    Value mValue;
};


//
// The polymorphic assignment access method
//
template <class Value>
void GenericValue::operator = (const Value &value)
{ safer_cast<TypedValue<Value> &>(*this) = value; }


}     // end namespace Security


#endif //_H_TYPEDVALUE

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