Define global function from within PHP namespace

It's possible but aside from being bad design, you will have to enclose your code within brackets for each namespace and won't be able to use namespace my_module; Instead it will have to be namespace my_module { ... }.

Example:

namespace my_module {

    function module_function()
    {
        // code
    }
}

namespace {
    // global namespace.

    function my_module()
    {
        // call your namespaced code
    }
}