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// Copyright (C) 2019 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
#ifndef ELEMENT_VALUE_H
#define ELEMENT_VALUE_H
#include <asiolink/io_address.h>
#include <cc/data.h>
#include <string>
namespace isc {
namespace data {
/// @brief Template class for converting a value encapsulated in the
/// @c Element object into a simple type.
///
/// The @c Element object provides a set of accessors to retrieve
/// values of different types it encapsulates. These methods
/// however can't be always used in template methods and classes.
///
/// Consider a template function which returns a value of a type
/// specified as template argument. In order to convert a value
/// held in the @c Element object it would have to conditionally
/// call this object's accessors to return the value of the
/// appropriate type. This would however fail to compile because
/// the compiler would check for all possible value types returned
/// by the @c Element accessors and report an error for those that
/// don't cast to the returned type.
///
/// This class provides a mechanism to extract the value of the
/// appropriate type from the @c Element object within the
/// template function. It comes with a number of class specializations
/// for various data types to be returned. The default implementation
/// calls @c Element::intValue and casts it to the returned type.
/// There are class specializations for @c double, @c bool and
/// @c string.
///
/// @tparam T Type of the value to be extracted.
template<typename T>
class ElementValue {
public:
/// @brief Function operator extracting an @c Element value as
/// integer.
///
/// @param el Element holding a value to be extracted.
T operator()(ConstElementPtr el) const {
return (static_cast<T>(el->intValue()));
}
};
/// @brief The @c ElementValue specialization for double.
template<>
class ElementValue<double> {
public:
/// @brief Function operator extracting an @c Element value as
/// double.
///
/// @param el Element holding a value to be extracted.
double operator()(ConstElementPtr el) const {
return (el->doubleValue());
}
};
/// @brief The @c ElementValue specialization for boolean.
template<>
class ElementValue<bool> {
public:
/// @brief Function operator extracting an @c Element value as
/// boolean.
///
/// @param el Element holding a value to be extracted.
bool operator()(ConstElementPtr el) const {
return (el->boolValue());
}
};
/// @brief The @c ElementValue specialization for string.
template<>
class ElementValue<std::string> {
public:
/// @brief Function operator extracting an @c Element value as
/// string.
///
/// @param el Element holding a value to be extracted.
std::string operator()(ConstElementPtr el) const {
return (el->stringValue());
}
};
/// @brief The @c ElementValue specialization for IOAddress.
template<>
class ElementValue<asiolink::IOAddress> {
public:
/// @brief Function operator extracting an @c Element value as
/// IOAddress.
///
/// @note This does NOT support empty string value.
///
/// @param el Element holding a value to be extracted.
asiolink::IOAddress operator()(ConstElementPtr el) const {
return (asiolink::IOAddress(el->stringValue()));
}
};
} // end of namespace isc::data
} // end of namespace isc
#endif // ELEMENT_VALUE_H
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