number of templated parameters in a boost::tuple

Question

I am using boost::tuple for my code.

Suppose that I want to store an equivalent of a structure having 3 members

  typedef boost::tuple< std::string, int, double > my_struct;

Is there any way of method to call on the tuple that will give me the number of members contained so in this case 3?

My goal here is to monitor when I increase the number of template parameters.

Can you elaborate a little more on "monitor increase the number of template parameters"? What sense is this going to make? You can only increase the number of parameters at compile time and if you pass a tuple around as `tuple` or `T` you will have to "loop" over it anyway. — pmr, Jun 28 '11 at 08:45
Not a direct answer to your question, but in C++11 `std::tuple_size::value` gives the number of parameters of an `std::tuple`. — Dennis Zickefoose, Jun 28 '11 at 09:00
pmr: Want to realize when I switch from tuple to tuple . I basically want to always assert this condition in some point of my code. — Abruzzo Forte e Gentile, Jun 28 '11 at 13:34

score 10 · Accepted Answer · answered Jun 28 '11 at 08:39

10

Use the ::boost::tuples::length<T>::value helper function.

answered Jun 28 '11 at 08:39

dalle

score 3 · Answer 2 · answered Jun 28 '11 at 08:37

3

Check the doccumentation here.

length<T>::value

gives the length of the tuple type T.

answered Jun 28 '11 at 08:37

Alok Save

score 2 · Answer 3 · answered Jun 28 '11 at 08:39

2

According to boost::tuple documentation what you are looking for is length<T>::value

answered Jun 28 '11 at 08:39

6502

3 Answers3