span class="op">-</span><span class="op">&gt;</span> <span class="kw">impl</span> <span class="ident">Future</span><span class="op">&lt;</span><span class="ident">Item</span> <span class="op">=</span> <span class="ident">S</span>, <span class="ident">Error</span> <span class="op">=</span> <span class="ident">S</span>::<span class="ident">Error</span><span class="op">&gt;</span>
<span class="kw">where</span>
    <span class="ident">S</span>: <span class="ident">hal</span>::<span class="ident">serial</span>::