(Re)named std::pair members

Question

Instead of writing town->first I would like to write town->name. Inline named accessors (Renaming first and second of a map iterator and Named std::pair members) are the best solutions I have found so far. My problem with named accessors is the loss of type safety: pair<int,double> may refer to struct { int index; double value; } or to struct { int population; double avg_temp; }. Can anyone propose a simple approach, perhaps something similar to traits?

I often want to return a pair or a tuple from a function and it is quite tiring to introduce a new type like struct city { string name; int zipcode; } and its ctor every time. I am thrilled to learn about boost and C++0x but I need a pure C++03 solution without boost.

Update

Re andrewdski's question: yes, a (hypothetical) syntax like pair<int=index, double=value> which would create a distinct type from pair<int=population, double=avg_temp> would meet your requirement. I do not even mind having to implement a custom pair/tuple template class ONCE and just passing a 'name traits' template argument to it approprietly when I need a new type. I have no idea how that 'name traits' would look like. Maybe it's impossible.

Answer 1

I don't see how you can possibly do better than

struct city { string name; int zipcode; }; 

There's nothing non-essential there. You need the types of the two members, your whole question is predicated around giving names to the two members, and you want it to be a unique type.

You do know about aggregate initialization syntax, right? You don't need a constructor or destructor, the compiler-provided ones are just fine.

Example: http://ideone.com/IPCuw

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Type safety requires that you introduce new types, otherwise pair<string, int> is ambiguous between (name, zipcode) and (population, temp).

In C++03, returning a new tuple requires either:

city retval = { "name", zipcode }; return retval; 

or writing a convenience constructor:

city::city( std::string newName, int newZip ) : name(newName), zipcode(newZip) {} 

to get

return city("name", zipcode); 

With C++0x, however, you will be allowed to write

return { "name", zipcode }; 

and no user-defined constructor is necessary.

Answer 2

I guess elaborating on

struct City : public std::pair<string, int> {   string& name() { return first; }   const string& name() const { return first; }   int& zip() { return second; }   int zip() const { return second; } }; 

is the closest you get to what youre looking for, althrough struct City { string name; int zipcode; } seems perfectly fine.