:example: ../examples/rolex

[#namespaces]

Note;; This section uses overrider containers, described in the
xref:headers.adoc[Headers and Implementation Files] section.

xref:BOOST_OPENMETHOD.adoc[BOOST_OPENMETHOD] defines a method in the current
namespace. xref:BOOST_OPENMETHOD_OVERRIDE.adoc[BOOST_OPENMETHOD_OVERRIDE] works
_across_ namespaces. Overriders are not required to be in the same namespace as
the method they override. The macro adds the overrider to a method that can be
called with the same arguments as the overrider, possibly located via argument
dependent lookup.

Overrider containers are added to the current namespace. It follows that the
same method can have overriders in multiple containers, in different namespaces.
This must be taken into account when calling an overrider explicitly. Let's put
Employee and Salesman in their own namespaces:

[source,c++]
----
include::{example}/4/roles.hpp[tag=content]
----

When we try to compile `salesman.cpp`:

[source,c++]
----
include::{example}/3/salesman.cpp[tag=content]
----

We get an error like:

```
error: implicit instantiation of undefined template
'sales::pay_boost_openmethod_overriders<
    double (boost::openmethod::virtual_ptr<const employees::Employee>)>
```

This is because the overrider container for `pay` in namespace `sales` is
specialized for `Salesman`, but not for `Employee`.  The overrider for Employee
is in a specialization of a different container, in namespace `employees`.

The solution is to qualify the overrider container with the `employees`
namespace:

[source,c++]
----
include::{example}/4/salesman.cpp[tag=content]
----
