General approach to overloading several similar functions

Question

I have this pattern in my code:

public:
    int start(const uint32_t channel);
    int stop(const uint32_t channel);
    void set_current_desc(uint32_t channel, uint64_t cdesc);
    // ...
private:
    const uint32_t channel_;

All functions take in the channel argument. I would like to provide this interface:

public:
    int start(const uint32_t channel);
    int start(void) { return start(channel_); } 
    int stop(const uint32_t channel);
    int stop(void) { return stop(channel_); }
    void set_current_desc(uint32_t channel, uint64_t cdesc);
    void set_current_desc(uint64_t cdesc) { set_current_desc(channel_, cdesc); }
    // ...
private:
    const uint32_t channel_;

Is there a general approach to doing this for all functions at once, or will I have to type it all out? I guess there exists some messy macro method but I would prefer a C++ non-macro solution.

Edit: The initial interface must remain due to backwards compatibility.

Answer 1

You can modify the methods to accept a std::optional with a default value of std::nullopt.

If the caller does not supply a channel (via the new interface) the channel_ member will be used.
If the caller supplies a channel (as you requested for backwards compatibility), it will be used.

This is done using the method std::optional::value_or.

#include <optional>
#include <iostream>
#include <cstdint>

class Test {
public:
    Test(uint32_t channel) : channel_(channel) {}

    void start(std::optional<uint32_t> channel = std::nullopt)
    {
        // Determine `cur_channel` to use:
        uint32_t cur_channel = channel.value_or(channel_);
        // Use `cur_channel` ...
        std::cout << "start, using channel: " << cur_channel << "\n";
    }
private:
    const uint32_t channel_;
};

int main() {
    Test test{ 333 }; // `channel_` member will be 333
    test.start();     // will use the `channel_` member of `test`
    test.start(5);    // will use 5 for the current channel (backwards compatibility)
}

Output:

start, using channel: 333
start, using channel: 5

Live demo

A similar approach can be used for the rest of your methods.