C static keyword vs C++ private scope?

As a sequel to this question: Best practice static C function or private C++ method

Which is the most adequate C++ replacement for

static void bar() {
}

appearing in a c module foo.c?

A private function in a class foo

class foo {
    void bar();
};

void foo::bar() {
    // ...
}

or as module private function in an unnamed namespace in the foo.cpp translation unit

namespace {
    void bar {
       // ...
    }
}

Or isn't there any way to compare these two on a semantical level?