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surfintheusa@yahoo.com · Guest

Hello,

Given the following:

template<typename T, size_t D>
class foo{
//...
foo<T, D> bar();
//...
};

template<typename T, size_t D>
foo<T, D> foo<T, D>::bar() { //... }

I'd like to add this:

template<T>
foo<T, 2> foo<T, 2>::bar() { //... }

Is that possible?

MSVC7.1 tells me "error C2244: 'foo<T,D>::bar' : unable to match
function definition to an existing declaration" while pointing to
foo<T, 2>::bar(). But if in my main I instantiate a foo<int, 2>, won't
that declare the foo<int, 2>::bar I want?

I've tried many things to fix/workaround/(please the compiler) but...
no cigar! :(

Thanks for your help!

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Gareth · Guest

You can't specialise member functions of a template class, but you can
use the following workaround:

#include <iostream>

template<typename T, size_t D>
class foo{

public:
foo<T, D> bar();
};

// Implementation of foo member functions which you want to
// specialise. Note that if these functions need to access non-public
// member data, then foo_impl needs to be a friend of foo.
template<typename T, size_t D>
struct foo_impl {

static foo<T, D> bar(foo<T,D>& f) {
std::cout << "generic" << std::endl;
return foo }
};

// Specialised implementation for D=2.
template<typename T>
struct foo_impl<T,2> {

static foo<T, 2> bar(foo<T,2>& f) {
std::cout << "D=2" << std::endl;
return foo }
};

// foo member function defers to implementation structure
template<typename T, size_t D>
foo<T, D> foo<T, D>::bar() { foo_impl<T,D>::bar(*this); }

int main() {

foo<int,1> f1;
f1.bar();

foo<int,2> f2;
f2.bar();
}

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Carl Barron · Guest

In article <1120816462.429729.66120 (AT) o13g2000cwo (DOT) googlegroups.com>,
Gareth <gareth_stockwell (AT) hotmail (DOT) com> wrote:

surfintheusa@yahoo.com · Guest

Thanks guys! That did it. :D

Now, I understand how this workaround works but I then have a follow-up
question: what's the good reason behind disallowing that? I have some
guesses about what was going wrong when I tried to compile my faulty
code but can't tell for sure. (If the answer is in a Meyers or Sutter
book, say so, I'll look it up.)

Thanks again!

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