s call aliases <a href="../../../reference/types/basic_outcome/has_error.html" class="api-reference"><code>bool has_error() const noexcept</code></a>.</p>

<p><em>Requires</em>: <code>operator==</code> must be a valid expression between <code>error_type</code> and <code>A</code>, or <code>A</code> is <code>void</code>. If <code>error_type</code> is <code>void</code>, then so must be <code>A</code>.</p>

<p><em>Complexity</em>: Whatever the underlying <code>operator==</code> has. Constexpr and noexcept of un