 {
</span><span class="boring">            calculation,
</span><span class="boring">            value: None,
</span><span class="boring">        }
</span><span class="boring">    }
</span><span class="boring">
</span><span class="boring">    fn value(&amp;mut self, arg: u32) -&gt; u32 {
</span><span class="boring">        match self.value {
</span><span class="boring">            Some(v) =&gt; v,
</span><span class="boring">            None =&gt; {
</span><span class="boring">                let v = (self.c