Re: Best way to pass a map-like container to a function

Am 31.08.2012 23:16, schrieb Marco Guazzone:
  > On Friday, August 31, 2012 12:13:36 AM UTC+2, Daniel Kr?gler wrote:
  > [cut]
  >
  >>> But, when the container is a map (or similar), what do you use?
  >>
  >> It certainly depends what you want to realize. There are clearly
  >> reasonable use-cases, where the associative container can be
  >> considered as a sequence of elements. This makes sense, because
  >> associative containers and unordered containers also satisfy the
  >> Container requirements.
  >>
  >>> Possibile candidates:
  >>>
  >>> 1. Two parameters: the first/last iterator pair:
  >>> map<...,...> m;
  >>> foo(m.begin(), m.end())
  >>
  >> Yes, this is IMO a very intuitive one. But you may need to explain
  >> what foo is going to do, before we speculate on that.
  >
  > You're right.
  > In fact, a possible issue with this signature is when you pass
  > iterators to multimap. 'foo', to work correctly, should not make
  > any assumption on the uniqueness of the first element of each pair.
  >
  > Maybe, in that case, it would be better to directly pass the
  > container?

The reason I was asking about foo is related to that. If foo is a very
general operation that can be performed without having a container at
hand, it makes very much sense in C++11 (without a proper range
concept) to provide an overload accepting a pair of iterators
representing a range.

  >>> 2. Four parameters: the first/last iterator pair representing the
  > [cut]
  >>
  >> I do'n see much value of this signature, but I certainly think
  >> that it would be nice to have a view on std::map that solely
  >> iterates over its keys or over its values. Java's Map interface
  >> provides these views and I would say that these two views are
  >> quite often used.
  >
  > Yes I agree. In addition to Java, there're many other languages
  > that have them (e.g., D, Perl, PHP and Python, just to name a
  > few). It's a pity that C++11 does not have them, or am I wrong?
  >
  > [cut]
  >
  >> I would consider as a different approach that accepts a range as
  >> argument. Certainly this approach is often very useful as well,
  >> for any container. The very advantage is that the caller has no
  >> chance to provide a wrong combination of iterator arguments.
  >
  > Interesting. I assume you're referring to Boost.Range, are you?

Yes, for example. I really think that C++ should introduce a range
template. Unfortunately it didn't make it into C++11.

If such a range template exists, it would be much simpler to add two
functions associated with the map types that return a range over they
key elements or over the mapped value elements.

HTH & Greetings from Bremen,

Daniel Kr?gler

--
      [ See http://www.gotw.ca/resources/clcm.htm for info about ]
      [ comp.lang.c++.moderated. First time posters: Do this! ]