Hello, I was reviewing the View Template Library (VTL) - see
http://www.zib.de/weiser/vtl/ ... and
have a few questions regarding Views
as applied to STL Maps.
I
was also wondering if Boost was planning to eventually provide a VTL-like
framework?
I'm looking for a type of View that provides read-only access
to an STL map, with only const iterators, but also provides limited insertion
and removal
access as well (as shown below):
This new limited
View-like map will only allow clients to iterate using const iterators, and also
provides only one public insert(const key&) and
one erase(const key&)
method.
These insert and erase member functions need to be
implemented as "Template Method Functions", as follows: (see Design
Patterns)
* Note: these are shown using the latest SGI STL implementation
(i.e., the
_M_t.insert_unique and _M_t.erase calls)
virtual bool
preInsert(const
value_type&)
{
return
true;
}
pair<iterator, bool> insert(const value_type&
x)
{
if(preInsert(x)
{
return _M_t.insert_unique(x);
}
return make_pair(end(), false);
// make compiler happy
}
virtual bool preErase(const
key_type&)
{
return
true;
}
size_type erase(const key_type&
x)
{
if(preErase(x)
{
return _M_t.erase(x);
}
return 0; // make compiler
happy
}
The preInsert and preErase methods are virtual Hook Methods,
and derived classes override these to add behavior to the (non-virtual) insert
and erase
functions..
Another nice addition to this map view
would be a const _Tp& operator[](const key_type& k) const function,
implemented something like this:
const _Tp& operator[](const
key_type& k) const
{
const_iterator i = lower_bound(k);
if(i == end() || key_comp(k, (*i).first)) // if i->first is >=
k
throw SearchError(k);
return
(*i).second;
}
* Note: this simple implementation assumes that the key
can be converted to a string in the constructor of the SearchError exception
object.
I have at least three Manager-like (Mediator) classes that
can use this pattern (i.e., derived from this Map View class) as well as others
that need
a vector view with a similar filtered design...
Thanks in
advance,
~Matt Verona
Houston,
Texas
USA