Re: [boost] Re : BOOST_FOREACH like macro for map

Subject: Re: [boost] Re : BOOST_FOREACH like macro for map
From: mobi phil (mobi_at_[hidden])
Date: 2009-10-20 18:42:19

Thanks for the replies... However

I forgot to put in my question that I am looking for a macro and not
template if possible, and for a solution as elegant as BOOST_FOREACH,
where you have to code as less as possible. It not (only :) ) that I
am lazy to write, but I think the resulting code would be easier to
read.

furthermore:
1. exception... throwing the exception removes the complexity of
writing but introduces the complexity of exception (writing code +
runtime).

2. pointer... use cases I would like to avoid pointers, as I have
other constraints to work with const references.

I was thinking all the day about this little "handicap" of the
std::map. One way would be to have the concept of invalid object of
the map data type that could be returned to satisfy the constraint of
the reference, and a "horrible" function like

bool return;
const data_type & data = map.find(key, bool)
if( return ) {
   //use the data
}
With this approach is that the "return" variable has to be declared.

with the form I proposed

BOOST_CONSTMAPFIND(aStringMap, "key", data)
{
     processResult( data );
}

the problem is that I do not know how to detect the type of data
knowing in the map object. I thought for the moment that BOOST_FOREACH
would "automatically" declare the type in the container (using
non-standard typeof for eg), but revisiting again BOOST_FOREACH
documentation i see  that it declares the type.
vector<int> v;
BOOST_FOREACH( int i, v) etc.

so it seems that if I declare the type of the data, my job becomes
easy, a sort of "problem solved"

const map<string, Mytype> & mymap = getMap();
//I changed the order of variables
BOOST_CONSTMAPFIND(const Mytype &data, "key", mymap)
{
    processResult(data);
}
and pair for non-const
BOOST_MAPFIND(Mytype &data, "key", mymap)

probably with some trick (probably sthg. similar used in
BOOST_FOREACH), one could merge theh two macros.

I am now two tired, but will write tomorrow the macro, test it, and
would be happy if boost would accept it into the macros family.

-- 
rgrds,
mobi phil
being mobile, but including technology
http://mobiphil.com