Variadic templates and multiple inheritance in c++11

Question

i'm trying to achieve something like this:

I have a templated base class which i want to inherit dynamically

template<typename A, typename B>
class fooBase
{
public:
    fooBase(){};
    ~fooBase(){};
};

desired method: (something like this, not really sure how to do it)

template <typename... Interfaces>
class foo : public Interfaces...
{
public:
    foo();
    ~foo();
}

and my goal is to have the foo class act like this:

second method:

class foo()
    : public fooBase<uint8_t, float>
    , public fooBase<uint16_t, bool>
    , public fooBase<uint32_t, int>
    // and the list could go on
{
    foo();
    ~foo();
}

with the second method the problem is that if i instantiate an foo object, it will inherit all the time those 3 base classes, i want to make it more generally and when instantiate a foo object, give it with variadic templates the parameters for the base classes, so that i can use the foo class for other types(maybe will inherit just one base class, maybe five)

Thank you

example for instantiating foo

foo<<uint8_t, float>, <uint16_t, bool>, <uint32_t, int>, /* and the list could go on and on */> instance

It looks like something similar was asked [here](http://stackoverflow.com/questions/27269603/variadic-template-based-multiple-inheritance-for-two-interacting-classes). — Ami Tavory, Mar 07 '16 at 10:16
Can you post an example of how you would like to instantiate `foo`? — TartanLlama, Mar 07 '16 at 10:18
sure, i want to instantiate it like this: foo instance<, , , /* and the list could go on and on */> — Mihai, Mar 07 '16 at 10:21
@mihaipop add the example to the question itself with the exact syntax you want to use — Piotr Skotnicki, Mar 07 '16 at 10:22
it doesn't make much sense with [this syntax](http://coliru.stacked-crooked.com/a/10abcc98ca8f9914) — Piotr Skotnicki, Mar 07 '16 at 10:40
The design of the inteface like this with multiple inheritance from same template class seems strange (and weird) to me. You can easily run into problems with member function when you use same time in that pair A or B. — Radek, Mar 07 '16 at 14:56

score 5 · Answer 1 · edited Mar 07 '16 at 12:00

5

Change foo to someting similar to this:

template<typename... Interfaces>
class foo : public Interfaces... {
  public:
    foo(Interfaces... ifaces) : Interfaces(ifaces)... {}

  };

edited Mar 07 '16 at 12:00

Niall

30,036
10
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answered Mar 07 '16 at 10:33

Jojje

381
3
13

score 5 · Accepted Answer · answered Mar 07 '16 at 13:03

You could try recursive variadic templates, taking 2 arguments at a time to add a derivation from fooBase.

It could be something like:

template<typename A, typename B>
class fooBase
{
public:
    fooBase(){};
    ~fooBase(){};
};

template<typename A, typename B, typename ... C>
class foo: public fooBase<A, B>, public foo<C ...> {
};

// termination version by partial specialization
template<typename A, typename B>
class foo<A, B>: public fooBase<A, B> {
};

You can then declare:

foo<uint8_t, float, uint16_t, bool, uint32_t, int> bar;

and bar will be a subobject of fooBase<uint8_t, float>, fooBase<uint16_t, bool> and fooBase<uint32_t, int>

Variadic templates and multiple inheritance in c++11

2 Answers2

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