Is there a convenient way to wrap std::pair as a new type?

Question

Often times I find myself using std::pair to define logical groupings of two related quantities as function arguments/return values. Some examples: row/col, tag/value, etc.

Answer 1

You can use some standard utility templates that help define the relation operators.

#include <utility>

http://www.sgi.com/tech/stl/operators.html

Requirements on types

The requirement for operator!= is that x == y is a valid expression
The requirement for operator> is that y < x is a valid expression
The requirement for operator<= is that y < x is a valid expression
The requirement for operator>= is that x < y is a valid expression

So basically it will automatically generate the other operators give < and == all you have to do is include <utility>

Answer 2

Unfortunately strong typedefs will not make it into C++0x, it has been given the classification of Not ready for C++0x, but open to resubmit in future.

Answer 3

A coworker pointed me to two possible solutions:

Using boost strong typedef as an improved version of the typedef. I'd never heard of this before, and it doesn't seem to really be part of any sub-library, just kind of floating.

Using a macro to generate the code needed for the different operators. This way I wouldn't have to explicitly write anything on a per definition level, just do something like DEFINE_PAIR_TYPE(Position, int, int, row, col);. This is probably closest to what I'm looking for, but it still feels kind of evil compared to some of the solutions presented by others.

Answer 4

This is what Boost.Tuple was made for.

But you should probably be using std::tuple now...

Answer 5

There's also the Boost::Operators library to automatically generate operator code. It's similar to the SGI library that Martin York suggested, but might be more portable.

Answer 6

You can still reuse the pair functionality by forwarding to it:

bool operator< ( const Position &a, const Position &b ) 
{
    return
        std::make_pair( a.row, a.col ) < std::make_pair( b.row, b.col );
}

Although you still end up with doing this for every operatory you need...