Re: template class and non-template class

From:

red floyd <redfloyd@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Sat, 25 Sep 2010 17:17:15 CST

Message-ID:

<1b8c1377-6120-4383-8a47-c9e6a0d268a2@l38g2000pro.googlegroups.com>

On Sep 24, 3:38 pm, ThosRTanner <ttann...@bloomberg.net> wrote:

I have a template class which I'd like to have a non-templated version
of - it's templated on a size_t which is currently a compile time
constant. I now need to make an almost identical class, except with
the size_t being a constructor parameter instead. This

template <size_t Size> class SomeClass {
     char data[Size];
....
     public:
        SomeClass() { };

};

and

class SomeClass {
     char *data;
....
     public:
     explicit SomeClass(size_t size) :
      data(new char[Size]) { }

};

more or less. The rest of the methods and implementation would be
exactly (for an appropriate meaning of exact) the same.

But I'd like to avoid having 2 copies of the code.

Any suggestions on how to go about this? (avoiding implementing the
template in terms of the non-template because the template class
shouldn't allocate memory dynamically)

Use a proxy class size of 0 as a marker. Comeau and g++ are both
quite happy with the below:

-- CUT HERE --
typedef unsigned size_t;

template< size_t Size > class FooData {
    char data[Size];
  public:
    FooData(size_t) { }
    operator char*() { return data; }
    operator char const * () const { return data; }
};

template<> struct FooData<0> {
    char *data;
  public:
    FooData(size_t sz) : data(new char[sz]) { }
    ~FooData() { delete[] data; }
    operator char*() { return data; }
    operator char const * () const { return data; }
};

template< size_t Size > struct Foo {
    FooData<Size> data;

    Foo(size_t sz = Size) : data(FooData<Size>(sz)) { }
};

void f()
{
    Foo<3> x;
    Foo<0> y(3);

    x.data[1] = 7;
    y.data[2] = x.data[1];
}

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