C++Talk.NET

Samee Zahur · Guest

I've really not been following recent developments in the upcoming
standard (or even boost lib for that matter) , so I'd like to
know if anything like this is under consideration:

For any function returning a heterogenous container like pair (or maybe
even tuple if a part of the new standard), I'd like to receive the
values into a bunch of 'loose' variables rather than having to declare
a pair object of an ugly type. For example, map::insert returns a pair,
so I'd like to be able to code this:

map<int,int> mymap;
map<int,int>::iterator it; //In real code iterator would be typedefed

//.. use it for some other task maybe, or not.

bool success;
lvpair(it,success)=mymap.insert(make_pair(4,1));

if(!success) cout<<"A value already exists for key 4"< else cout<<"Data inserted successfully"< //... some other code

This allows me to avoid extra declarations and avoid use of
generic identifier names more easily ( if(!success)...
rather than if(!res.second)... )

So I was thinking if a light-weight addition was possible (if
not already proposed).
--------------------------------------------------------------
template {
A& aref;
B& bref;
public:
lvalue_pair(A& ainit,B& binit) : aref(ainit), bref(binit) {}
template <class Asrc, class Bsrc>
lvalue_pair& operator=(std::pair<Asrc,Bsrc> p)
{aref=p.first; bref=p.second;return *this;}
template <class Asrc, class Bsrc>
lvalue_pair& operator=(const lvalue_pair& p)
{aref=p.aref; bref=p.bref; return *this;}
};

template <class A,class B> lvalue_pair<A,B> lvpair(A& ainit,B& binit)
{return lvalue_pair<A,B>(ainit,binit);}
---------------------------------------------------------------
Seemed like a pretty useful addition to me (could be extended
to tuples), although it needs objects to be assignable.

Samee

PS. seriously, does the stl map::value_type have to be a plain
pair object? I'd like something at least derived from it instead,
so that I have codes like it->key,it->value rather than it->first,
it->second. That way it could simply have key and value aliased/
referenced to first and second. Old codes don't complain, new ones
look better :)

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Ben Hutchings · Guest

I think what you're looking for is std::tr1::tie (aka boost::tie).

Ben.

--
Ben Hutchings
Never attribute to conspiracy what can adequately be explained by stupidity.

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David Abrahams · Guest

"Samee Zahur" <samee.zahur (AT) gmail (DOT) com> writes:

Samee Zahur · Guest

Thanks, really saved my day.
It was getting somewhat common to write this little thing up wherever I
use these utilities. Good to know that I won't have to very soon. Say,
how soon are we likely to see these things implemented?

Samee

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chris jefferson · Guest

Samee Zahur wrote:

David Abrahams · Guest

"Samee Zahur" <samee.zahur (AT) gmail (DOT) com> writes: