Re: [Boost-users] tuple

Subject: Re: [Boost-users] tuple
From: Jeremiah Willcock (jewillco_at_[hidden])
Date: 2010-04-22 17:15:41

On Thu, 22 Apr 2010, luca formaggia wrote:

> Hello,
> 
> someone could tell me what is wrong in this piece of code
> 
> #include "boost/tuple/tuple.hpp"
> using namespace boost::tuples;
> int main(){
> Â Â Â Â Â Â Â  tuple<int, double> t2();
> Â Â Â Â Â Â Â  get<0>(t2)=int(10);
> }
> 
> I get the following error message:
> 
> g++ try.cpp
> try.cpp: In function ‘int main()’:
> try.cpp:5: error: no matching function for call to ‘get(boost::tuples::tuple<int, double, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type,
> boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> (&)())
> 
> In the tutorial it is written that tuple<int, double> t2() should construct the object via the default constructor.

This syntax is not correct.  "tuple<int, double> t2();" declares a 
function named t2 that returns a tuple<int, double>, not an actual tuple. 
Leave off the extra parentheses to get a working version.

> Why I cannot access the first element (it works if I give an initial 
> value, for instance using  tuple<int, double> t2(1);  I get a similar 
> error if I use the method get<N>() instead of the function.

Adding an initial value disambiguates the statement so it is no longer a 
function declaration.  The version of get you use does not matter to this 
problem.

-- Jeremiah Willcock