Re: [boost] [type_map] Interest in container indexed by type?

From: Larry Evans (cppljevans_at_[hidden])
Date: 2005-10-31 08:04:42

Hi Tony,

On 10/31/2005 04:12 AM, Tony D wrote:
[snip]
> block for reusable code.  Effectively, code can use
> "type_maps" to handle an arbitrary structure, without
> needing to know member identifiers, and gets the speed
Yes, but you'd need to know the types, and if a type
is duplicated, as you say below, it would have to be
wrapped in some class to make it unique.
[snip]
> benefit of compile-time access resolution.
> int main()
> {
>     NS::type_map<int, string> tmid;
>     tmid = 3;
>     tmid = "hello";
>     string s = tmid;
>     cout << (int)tmid << ' ' << (string)tmid << ' '
>          << s << endl;
>     cout << sizeof(tmid) << " vs " << sizeof(int)
>          << '+' << sizeof(string) << endl;
> }
So if I had:
<---------------
struct sname_t
{ string first_m;
   string last_m;
};
sname_t a_sname;
a_sname.first_m="first";
a_sname.last_m="last";
 >---------------
then, to convert this to using typemaps, I would do:
<---------------
struct fname_t: public string{...};
struct lname_t: public string{...};
NS:type_map<fname_t,lname_t> mname_t;
mname_t a_mname;
a_mname = fname_t("first");
a_mname = lname_t("last");
 >--------------

So I don't see that I've gained much, at least in
this case.
[snip]
> cataloging errors.  To store several data items of the
> same type, simply wrap each instance in a distinct
> class (possibly using the template w/ unique number
> idiom).
[snip]
-regards,
Larry