Comments inline ... Jean-Louis Leroy schrieb:
First there's the warning :
1>c:\program
files\boost\boost_1_39\boost\fusion\view\transform_view\detail\deref_impl.hpp(42)
: warning C4172: returning address of local variable or temporary 1> c:\program
etc etc etc
I assume you return the plain argument type (that is a reference) in your triple2::result meta-function. If that's the case, simply wrap the argument in a remove_reference. E.g. struct triple2 { //... template<typename Self, typename Arg> struct result<Self(Arg)>: boost::remove_reference<Arg> {}; };
Also, I see that transform returns a view. I need a proper vector that is distinct from the input vector. Here's a bit of context. I am building a recipient for one row in a database query. I have a vector of Exprs, one for each column in the select. Expr has a type member. I want to make a vector with an element for each Expr, initialized to the type's default value (as per type()).
I.e. something like this :
struct f { /* ... */ template<typename Expr> operator ()(Expr) { return typename Expr::type(); } typedef result_of::transform<SelectList, f>::type row_type; row_type row; transform(select.exprs, row); // type of select.exprs is SelectList std::deque<row_type> results; while (data) { for_each(row, read_fun(...)); results.push_back(row); }
Alas row_type is going to be a view :-/
simply convert the view (type!) back to a vector using fusion::result_of::as_vector. using namespace boost::fusion; result_of::as_vector<result_of::transform<SelectList,f>::type>::type vec; -Christopher