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/******************************************************************************
* Copyright (C) 2016 Kitsune Ral <kitsune-ral@users.sf.net>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#pragma once
namespace QMatrixClient
{
/**
* @brief A crude wrapper around a container of pointers that owns pointers
* to contained objects
*
* Similar to vector<unique_ptr<>>, upon deletion, this wrapper
* will delete all events contained in it. This wrapper can be used
* over Qt containers, which are incompatible with unique_ptr and even
* with QScopedPointer (which is the reason of its creation).
*/
template <typename ContainerT>
class Owning : public ContainerT
{
public:
Owning() = default;
Owning(Owning&) = delete;
Owning(Owning&& other) = default;
Owning& operator=(Owning&& other)
{
assign(other.release());
return *this;
}
~Owning() { cleanup(); }
void assign(ContainerT&& other)
{
if (&other == this)
return;
cleanup();
ContainerT::operator=(other);
}
/**
* @brief returns the underlying container and releases the ownership
*
* Acts similar to unique_ptr::release.
*/
ContainerT release()
{
ContainerT c;
ContainerT::swap(c);
return c;
}
private:
void cleanup() { for (auto e: *this) delete e; }
};
/**
* @brief Lookup a value by a key in a varargs list
*
* This function template takes the value of its first argument (selector)
* as a key and searches for it in the key-value map passed in a varargs list
* (every next pair of arguments forms a key-value pair). If a match is found,
* the respective value is returned; if no pairs matched, the last value
* (fallback) is returned.
*
* All options should be of the same type or implicitly castable to the
* type of the first option. Note that pointers to methods of different
* classes are of different object types, in particular.
*
* Below is an example of usage to select a parser depending on contents of
* a JSON object:
* {@code
* auto parser = lookup(obj.value["type"].toString(),
* "type1", fn1,
* "type2", fn2,
* fallbackFn);
* parser(obj);
* }
*
* The implementation is based on tail recursion; every recursion step
* removes 2 arguments (match and option). There's no selector value for the
* fallback option (the last one); therefore, the total number of lookup()
* arguments should be even: selector + n key-value pairs + fallback
*
* @note Beware of calling lookup() with a <code>const char*</code> selector
* (the first parameter) - most likely it won't do what you expect because
* of shallow comparison.
*/
template <typename ValueT, typename SelectorT, typename KeyT, typename... Ts>
ValueT lookup(SelectorT selector, KeyT key, ValueT value, Ts... remainingMapping)
{
if( selector == key )
return value;
// Drop the failed key-value pair and recurse with 2 arguments less.
return lookup(selector, remainingMapping...);
}
template <typename SelectorT, typename ValueT>
ValueT lookup(SelectorT/*unused*/, ValueT fallback)
{
return fallback;
}
} // namespace QMatrixClient
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