In C++, templates allow us to write highly flexible and reusable code. However, templates are typically resolved at compile-time, and it can be challenging to deserialize or read template code at runtime. In this blog post, we will explore how to use recursive templates to achieve template code deserialization in C++.

Template Code Deserialization

Template code deserialization refers to the process of reading and interpreting template code at runtime, allowing us to dynamically generate and use templates based on user input or external data. This can be especially useful in scenarios where we need to create objects or apply algorithms based on runtime parameters.

Recursive Template Approach

To achieve template code deserialization, we can use a recursive template approach. This technique involves defining a recursive template structure that matches the input code’s structure.

Let’s consider an example where we want to deserialize a template function that adds two numbers:

template <typename T>
T Add(T a, T b) {
    return a + b;
}

We can define a recursive template structure that reflects the structure of the Add function:

template <typename T>
struct Deserializer {
    static T Deserialize(const std::string& code) {
        // Deserialize code and generate template
        // logic goes here
    }
};

template <typename T>
struct Deserializer<T (*)(T, T)> {
    static T Deserialize(const std::string& code) {
        // Handle function template
        // logic goes here
    }
};

template <typename T>
struct Deserializer<T> {
    static T Deserialize(const std::string& code) {
        // Handle type template
        // logic goes here
    }
};

In this example, we define a primary template Deserializer<T> that handles deserialization of simple types, such as int or float. We also specialize the Deserializer template for function templates using the partial specialization syntax Deserializer<T (*)(T, T)>. This specialization handles deserialization of function templates, such as the Add function.

The Deserialize function in each template specialization should implement the deserialization logic specific to that template type. This could involve parsing the code string, extracting template parameters, and generating the desired template code.

Usage Example

int main() {
    std::string code = "Add(int a, int b)";
    int result = Deserializer<decltype(Add)>::Deserialize(code)(3, 4);
    std::cout << "Result: " << result << std::endl;
    return 0;
}

In the above usage example, we assume the code string contains the template function name and its arguments. We use the decltype keyword to determine the function’s type and pass it to the Deserializer template. The Deserialize function of the Deserializer template will perform the necessary deserialization logic to generate the template function based on the provided code.

Conclusion

Using recursive templates, we can achieve template code deserialization in C++. This technique gives us the flexibility to dynamically generate and use templates based on runtime input or external data. While the example in this blog post demonstrated template function deserialization, the same approach can be extended to handle other template structures.

#C++ #TemplateDeserialization