/span>  <span class="k">static</span> <span class="k">constexpr</span> <span class="kt">bool</span> <span class="n">enable_outcome_inputs</span> <span class="o">=</span> <span class="nb">false</span><span class="p">;</span>
  
  <span class="c1">// `X` will be the raw input form of `U`. It must return a `T`.
</span><span class="c1"></span>  <span class="k">template</span><span class="o">&lt;</span><span class="k">class</span><span class="err"> </span><span class="nc">X</span><span class="o">&gt;</span> <spa