The second notable interaction occurs with non-function symbols. In the context of this section, the important ones are function objects (and lambdas).

Argument-dependent lookup will not consider non-function symbols. This means that a function object or a lambda must be either visible to an unqualified lookup or need to be fully qualified.

\begin{box-note}

\footnotesize Example demonstrating a lambda stored in an inline variable that can only be invoked through a qualified call.

\cppfile{code_examples/theory/adl_nonfunc_code.h}

\end{box-note}

Finally, discovering a non-function symbol during the unqualified lookup phase will prevent ADL completely.

\begin{box-note}

\footnotesize Example demonstrating a non-function object preventing ADL, making a friend function impossible to invoke.

\cppfile{code_examples/theory/adl_shutdown_code.h}

\end{box-note}