Re: local classes and boost::function
Seungbeom Kim wrote:
John Moeller wrote:
gast128@hotmail.com wrote:
Unfortunately the actual class is a template and so the sources are in
header file. I don't know if this anonymous namespace is scalable to
header files. At least the defintion of the functor si not at the same
place where it is used.
In that case, an anonymous namespace would be a bad idea, especially
considering how it's defined. If you included a file containing this
anonymous namespace in several files, you would, in essence, create
several definitions of the same "Local" class, thus violating the ODR.
Anonymous namespaces in different translation units are different
namespaces, so in that case you would create several different classes
named "Local" in different namespaces (for example, _anonymous_A::Local
and _anonymous_B::Local) and not several different definitions of the
same class. It's not a violation of ODR.
Not directly, but imagine this:
namespace {
struct x { };
}
struct y {
x an_x;
};
This put into a header will yield different definitions of struct y every
time it is compiled, because y's x member is something different, too. You
could instead put y into the anon namespace, too or move x to a named
namespace.
If you put y into the anonymous namespace, you again can't use it in a
definition of anything that might be included into more than one
translation unit, i.e. the same problem applies and is only shifted a bit.
This then only leaves the possibility to define non-interface defining
code, limiting it somewhat for the OP's use.
Stick the utility classes into a namespace, e.g. called 'detail' so that it
is obvious that it is an implementation detail and not part of the public
interface.
Uli
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