LibWeb: Add DOM::ExceptionOr<T> container

Much like AK::Result this carries either a DOM::DOMException or regular
return value and will be used by DOM functions for exceptions that
should be thrown.

Userland/Libraries/LibWeb/DOM/ExceptionOr.h

@@ -0,0 +1,110 @@
+/*
+ * Copyright (c) 2021, Linus Groh <mail@linusgroh.de>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/NonnullRefPtr.h>
+#include <AK/Optional.h>
+#include <AK/RefPtr.h>
+#include <LibWeb/DOM/DOMException.h>
+
+namespace Web::DOM {
+
+template<typename ValueType>
+class ExceptionOr {
+public:
+    ExceptionOr(const ValueType& result)
+        : m_result(result)
+    {
+    }
+
+    ExceptionOr(ValueType&& result)
+        : m_result(move(result))
+    {
+    }
+
+    ExceptionOr(const NonnullRefPtr<DOMException> exception)
+        : m_exception(exception)
+    {
+    }
+
+    ExceptionOr(ExceptionOr&& other) = default;
+    ExceptionOr(const ExceptionOr& other) = default;
+    ~ExceptionOr() = default;
+
+    ValueType& value()
+    {
+        return m_result.value();
+    }
+
+    ValueType release_value()
+    {
+        return m_result.release_value();
+    }
+
+    const DOMException& exception() const
+    {
+        return *m_exception;
+    }
+
+    bool is_exception() const
+    {
+        return m_exception;
+    }
+
+private:
+    Optional<ValueType> m_result;
+    RefPtr<DOMException> m_exception;
+};
+
+template<>
+class ExceptionOr<void> {
+public:
+    ExceptionOr(const NonnullRefPtr<DOMException> exception)
+        : m_exception(exception)
+    {
+    }
+
+    ExceptionOr() = default;
+    ExceptionOr(ExceptionOr&& other) = default;
+    ExceptionOr(const ExceptionOr& other) = default;
+    ~ExceptionOr() = default;
+
+    const DOMException& exception() const
+    {
+        return *m_exception;
+    }
+
+    bool is_exception() const
+    {
+        return m_exception;
+    }
+
+private:
+    RefPtr<DOMException> m_exception;
+};
+
+}