Re: Is it legal to use maps with refrences ?

Goran <>
Fri, 25 Jun 2010 02:54:44 CST
On Jun 25, 2:50 am, Timothy Madden <> wrote:


My compiler complains if I try to declare

      std::map<unsigned, RECT const &>::iterator it

in the argument list for a function declaration.

So I would like to know if it is legal to declare such a container.

I don't think so. The problem is, that would produce "references to
references" in quite a bit of places.

So pointers are in order. You might want to wrap the pointer in a
reference-like object and use that in your map ?

( NB: very limited usability; compiled with head-compiler and tested
with head-debugger ;-) )

class rect_holder
  rect_holder(const RECT& p) :_p(&p) {}
  operator const RECT&() const { assert(p); return *p; }
  const RECT* _p;

std::map<unsigned, const rect_holder> mmm;

rect_holder gives you "copyability", and you can even do e.g.

const RECT& r = your_map[1];

But note also: with a map, if your value type is not const, you can't
use operator[] like so:

your_map[key] = value;

So IMO it's not a good idea to use const value type. You should
instead pass const map around.


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