CODEWITHSUNDEEP
c++templatesstl
user2080366
user2080366

Reputation: 25

Converting dataset to any stl container

I have some data sets of known types that I'd like to convert into stl containers by specifying the desired types like this:

Dataset dataset0(....);
Dataset dataset1(....);
Dataset dataset2(....);

int i = dataset0.convert<int>();

vector<int> vi = dataset1.convert<vector<int> >();

pair<vector<bool>, pair<bool, float> > complex = dataset2.convert<vector<pair<vector<bool>, pair<bool, float> >> >();

therefor I have made the following function in my Dataset class:

class Dataset
{
....
    template<typename T>
    T convert();
};

It's trivial to implement for the basic types like this:

template<>
int convert<int>()
{
    return int(/*implementation*/);
}

But the question is, how can I do this for stl containers of any type. Something like this:

template<>
vector<T> convert<vector<T> >() // ?? does not compile. where would T come from?
{
    vector<T> ret;
    for(/* Loop determined from data */)
    {
        ret .push_back(convert<T>())
    }
    return ret;
}

Upvotes: 1

Views: 175

Answers (2)

n. m. could be an AI
n. m. could be an AI

Reputation: 120049

One would be tempted to simply say

template<typename T>
vector<T> convert<vector<T> >()

This however would mean that you are trying to define a partial specialization of a function template. This is not allowed in C++.

There's no easy work around. The only advice I can give is naming different variants of convert differently (convert_to_vector etc). If you wish to keep naming consistency, you can define a class template Convertor and specialize it for different types, using different convertor functions. For instance:

class Dataset
{
    template<typename T>
        T convert();

    template<typename T>
        vector<T> convert_to_vector() { return vector<T>(); }
    template<typename T>
        list<T> convert_to_list() { return list<T>(); }
};

template<>
int Dataset::convert<int>() { return 0; }

template<>
double Dataset::convert<double>() { return 0; }

template <typename T> class Convertor
{
  public: T convert (Dataset& d) { return d.convert<int>(); }
};

template <typename T> class Convertor< vector<T> >
{
  public: vector<T> convert (Dataset& d) { return d.convert_to_vector<T>(); }
};

template <typename T> class Convertor< list<T> >
{
  public: list<T> convert (Dataset& d) { return d.convert_to_list<T>(); }
};

Then use it like Convertor<some-type>.convert(data).

Upvotes: 2

kiriloff
kiriloff

Reputation: 26333

Maybe this would do

template<typename T>
vector<T> convert();

if you mentionned vectoras an example and want to use other type of containers also, then you should define a `container_type convert_to_container_type()' method for each of them

Upvotes: 0

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