Re: Proper use of templated containers as class members

From:

Victor Bazarov <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Thu, 04 Dec 2008 10:15:51 -0500

Message-ID:

<gh8s77$9m1$1@news.datemas.de>

Per wrote:

I am finding myself doing the following rather often when I have
template containers in classed, e.g. stl::map

For example:

class Foo
{
public:
   typedef std::map<std::string, int> direcory_t;
   //More typedefs of the same style...
private:
   directory_t directory_m;
   //More members of the same style...
public:
   //Constructors and stuff
   const directory_t& directory() const {return directory_m;}
};

The question is what is your opinion on typedefing like this. At the
same time as it saves a lot of typing. After a while there are very
many types in a project. And in the end can get confusing about what
the type really contains. Classes should of course hide their
implementation but it seams very stupid not to have read access
directly to a member. If I didn't have that I have to bloat the class
with wrapper functions for the members. And not using typedefs would
lead to an awful lot of typing.

I use this approach everywhere. It's an abstraction. The users of your
class will use "Foo::directory_t" when they need the type. The main
thing is not saving typing (although it's a nice side effect) but the
ability to change what 'directory_t' means with a single line, and not
to worry about changing the rest of the code that uses it. That's the
whole idea behind typedefs. It doesn't matter how they are defined, as
a namespace member or as a class member.

V
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