Abstract Values, SimBody style

abstract_value.cc

#include <cassert>
#include <iostream>
#include <memory>
#include <string>

template<typename T> class Value;

class AbstractValue {
 public:
  AbstractValue() {}
  virtual ~AbstractValue() {}
  virtual std::string GetTypeName() const;
  // Returns the value if it’s of type Value<T>, or else asserts.
  template<typename T> const T& GetValue() const {
    const Value<T>* value = dynamic_cast<const Value<T>*>(this);
    assert(value != nullptr);
    return value->value();
  }
};

std::string AbstractValue::GetTypeName() const {
	return "abstract";
}

template<typename T> class Value : public AbstractValue {
 public:
  explicit Value(std::unique_ptr<T> value): value_(std::move(value)){}
  virtual ~Value() {}

  virtual const T& value() const { return *value_; }

  std::string GetTypeName() const override { return typeid(T).name(); }

 private:
  std::unique_ptr<T> value_;
};

int main(int argc, char* argv[]) {
  Value<double> pi(std::unique_ptr<double>(new double(3.14159)));
  AbstractValue* abstract = &pi;
  std::cout << abstract->GetValue<double>() << std::endl;
}