Source/WebCore/dom/ExceptionOr.h

/*

Copyright (C) 2016-2017 Apple Inc. All rights reserved.

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are met:
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    notice, this list of conditions and the following disclaimer.
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    notice, this list of conditions and the following disclaimer in the
    documentation and/or other materials provided with the distribution.

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WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
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*/

#pragma once

#include "Exception.h"
#include <wtf/CrossThreadCopier.h>
#include <wtf/Expected.h>

namespace WebCore {

template<typename ReturnType> class ExceptionOr {
public:
    ExceptionOr(Exception&&);
    ExceptionOr(ReturnType&&);
    template<typename OtherType> ExceptionOr(const OtherType&, typename std::enable_if<std::is_scalar<OtherType>::value && std::is_convertible<OtherType, ReturnType>::value>::type* = nullptr);

    bool hasException() const;
    const Exception& exception() const;
    Exception&& releaseException();
    const ReturnType& returnValue() const;
    ReturnType&& releaseReturnValue();
    
private:
    Expected<ReturnType, Exception> m_value;
};

template<typename ReturnReferenceType> class ExceptionOr<ReturnReferenceType&> {
public:
    ExceptionOr(Exception&&);
    ExceptionOr(ReturnReferenceType&);

    bool hasException() const;
    const Exception& exception() const;
    Exception&& releaseException();
    const ReturnReferenceType& returnValue() const;
    ReturnReferenceType& releaseReturnValue();
    
private:
    ExceptionOr<ReturnReferenceType*> m_value;
};

template<> class ExceptionOr<void> {
public:
    ExceptionOr(Exception&&);
    ExceptionOr() = default;

    bool hasException() const;
    const Exception& exception() const;
    Exception&& releaseException();

private:
    Expected<void, Exception> m_value;
};

ExceptionOr<void> isolatedCopy(ExceptionOr<void>&&);

template<typename ReturnType> inline ExceptionOr<ReturnType>::ExceptionOr(Exception&& exception)
    : m_value(makeUnexpected(WTFMove(exception)))
{
}

template<typename ReturnType> inline ExceptionOr<ReturnType>::ExceptionOr(ReturnType&& returnValue)
    : m_value(WTFMove(returnValue))
{
}

template<typename ReturnType> template<typename OtherType> inline ExceptionOr<ReturnType>::ExceptionOr(const OtherType& returnValue, typename std::enable_if<std::is_scalar<OtherType>::value && std::is_convertible<OtherType, ReturnType>::value>::type*)
    : m_value(static_cast<ReturnType>(returnValue))
{
}

template<typename ReturnType> inline bool ExceptionOr<ReturnType>::hasException() const
{
    return !m_value.has_value();
}

template<typename ReturnType> inline const Exception& ExceptionOr<ReturnType>::exception() const
{
    return m_value.error();
}

template<typename ReturnType> inline Exception&& ExceptionOr<ReturnType>::releaseException()
{
    return WTFMove(m_value.error());
}

template<typename ReturnType> inline const ReturnType& ExceptionOr<ReturnType>::returnValue() const
{
    return m_value.value();
}

template<typename ReturnType> inline ReturnType&& ExceptionOr<ReturnType>::releaseReturnValue()
{
    return WTFMove(m_value.value());
}

template<typename ReturnReferenceType> inline ExceptionOr<ReturnReferenceType&>::ExceptionOr(Exception&& exception)
    : m_value(WTFMove(exception))
{
}

template<typename ReturnReferenceType> inline ExceptionOr<ReturnReferenceType&>::ExceptionOr(ReturnReferenceType& returnValue)
    : m_value(&returnValue)
{
}

template<typename ReturnReferenceType> inline bool ExceptionOr<ReturnReferenceType&>::hasException() const
{
    return m_value.hasException();
}

template<typename ReturnReferenceType> inline const Exception& ExceptionOr<ReturnReferenceType&>::exception() const
{
    return m_value.exception();
}

template<typename ReturnReferenceType> inline Exception&& ExceptionOr<ReturnReferenceType&>::releaseException()
{
    return m_value.releaseException();
}

template<typename ReturnReferenceType> inline const ReturnReferenceType& ExceptionOr<ReturnReferenceType&>::returnValue() const
{
    return *m_value.returnValue();
}

template<typename ReturnReferenceType> inline ReturnReferenceType& ExceptionOr<ReturnReferenceType&>::releaseReturnValue()
{
    return *m_value.releaseReturnValue();
}

inline ExceptionOr<void>::ExceptionOr(Exception&& exception)
    : m_value(makeUnexpected(WTFMove(exception)))
{
}

inline bool ExceptionOr<void>::hasException() const
{
    return !m_value.has_value();
}

inline const Exception& ExceptionOr<void>::exception() const
{
    return m_value.error();
}

inline Exception&& ExceptionOr<void>::releaseException()
{
    return WTFMove(m_value.error());
}

inline ExceptionOr<void> isolatedCopy(ExceptionOr<void>&& value)
{
    if (value.hasException())
        return isolatedCopy(value.releaseException());
    return { };
}

}

namespace WTF {
template<typename T> struct CrossThreadCopierBase<false, false, WebCore::ExceptionOr<T> > {
    typedef WebCore::ExceptionOr<T> Type;
    static Type copy(const Type& source)
    {
        if (source.hasException())
            return crossThreadCopy(source.exception());
        return crossThreadCopy(source.returnValue());
    }
};
}