Question

Is there a good way in C++ to implement (or fake) a type for a generic vector of vectors?

Ignore the issue of when a vector of vectors is a good idea (unless there’s something equivalent which is always better). Assume that it does accurately model the problem, and that a matrix does not accurately model the problem. Assume also that templated functions taking these things as parameters do need to manipulate the structure (e.g. calling push_back), so they can’t just take a generic type supporting [][].

What I want to do is:

template<typename T> typedef vector< vector<T> > vecvec;  vecvec<int> intSequences; vecvec<string> stringSequences; 

but of course that’s not possible, since typedef can’t be templated.

#define vecvec(T) vector< vector<T> > 

is close, and would save duplicating the type across every templated function which operates on vecvecs, but would not be popular with most C++ programmers.

Answer 1

You want to have template-typedefs. That is not yet supported in the current C++. A workaround is to do

template<typename T> struct vecvec {      typedef std::vector< std::vector<T> > type; };  int main() {     vecvec<int>::type intSequences;     vecvec<std::string>::type stringSequences; } 

In the next C++ (called c++0x, c++1x due to 2010), this would be possible:

template<typename T> using vecvec = std::vector< std::vector<T> >;