Non-member non-friend interfaces
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Reduce dependencies on internal class details and improve encapsulation.
non_member on lines 15–18 is also logically part of
foo’s interface, yet has been defined as a non-member because it
can be implemented in terms of
member. This approach
by reducing the number of functions that are dependent on the
private members of a class.
On line 24, argument-dependent lookup (ADL) allows us to call
non_member without qualifying it with the
ns namespace. The ADL
rule specifies that the name of a function will be looked up
in the namespaces of its arguments. As we are passing an
non_member, the function is found in the