AMDG Bill Buklis wrote:
Frequently I have to write comparison functions (usually of the "less" variety) that involve multiple keys or members of a struct. For example:
struct s { A a; B b; C c; D d; // there may be other members not used in the comparison };
// operator< function or an equivalent function object bool operator<( const s& lhs, const s& rhs ) { if( lhs.a < rhs.a ) return(true); else if( lhs.a == rhs.a ) { if( lhs.b < rhs.b ) return(true); else if( lhs.b == rhs.b ) //and so on... } return(false); }
This gets quite repetitive, especially if I have to write alternate sort orders (e.g. b,a,c,d or c,d,a,b)
I'm thinking there has to an easier way to do this or a way to do a generic algorithm for this. Is there anything in boost that would help?
I had an idea that one might be able to fill a vector with binders for each element and then call lexicographical_compare, but I'm not sure how to make it work.
Boost.Fusion provides several ways to do this.
#include