safe_query.cpp

#include <iostream>
#include <sstream>
#include <array>
using namespace std;


enum class State {
    FINISHED, UNFINISHED
};

template<int N, State state>
class SafeQuery {
private:
    stringstream ss;

public:
};

template<int N>
class SafeQuery<N, State::UNFINISHED> {
private:
    stringstream ss;

public:
    SafeQuery(stringstream &&ss):
            ss(move(ss)){
    }

    SafeQuery<N + 1, State::FINISHED> equals(string columnName) {
        ss << columnName << " = ? ";
        return SafeQuery<N + 1, State::FINISHED>(move(ss));
    }
};

template<int N>
class SafeQuery<N, State::FINISHED> {
private:
    stringstream ss;

public:

    SafeQuery(stringstream &&ss):
        ss(move(ss)) {
    }

    SafeQuery<N, State::UNFINISHED> and_() {
        ss << " AND ";
        return SafeQuery<N, State::UNFINISHED>(move(ss));
    }

    const string format(const array<string, N> &args) const {
        string s = ss.str();
        size_t index = 0;
        for (int i = 0; i < N; i++) {
            index = s.find("?", index);
            s.replace(index, 1, args[i]);
            index += args[i].length();
        }
        return s;
    }
};

using EmptyQuery = SafeQuery<0, State::UNFINISHED>;

template<int N>
using FinishedQuery = SafeQuery<N, State::FINISHED>;

static EmptyQuery emptyQuery() {
    return SafeQuery<0, State::UNFINISHED>(stringstream());
};


int main() {
//    emptyQuery().equals("folder_type").equals("unread_count"); // compile error!
//    emptyQuery().equals("folder_type").and_().and_(); // compile error!
    FinishedQuery<2> query = emptyQuery().equals("folder_type").and_().equals("unread_count");

    
//    string sqliteQuery = query.format({"4", "0", "whatever"}); // compile error!
    string sqliteQuery = query.format({"4", "0"});
    cout << sqliteQuery;
    return 0;
}