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#pragma once
#include <Core/Settings.h>
#include <Storages/MergeTree/MergeTreeSettings.h>
//
// Settings from different classes (Settings, MergeTreeSettings) can coexist in the same "namespace".
// This is, for example, required to define settings constraints inside user profiles.
// `resolveSetting(full_name)` is used to resolve setting name and choose which class is to be used.
// Templated lambda syntax should be used:
//
// return resolveSetting(name, [] <typename T> (std::string_view name, SettingsType<T>)
// {
// return T::castValueUtil(name, value); // T will be deduced into `Settings`, `MergeTreeSettings`, ...
// });
//
namespace DB
{
constexpr std::string_view MERGE_TREE_SETTINGS_PREFIX = "merge_tree_";
template <typename T> struct SettingsType {};
// Resolve setting name and call function `f` back with short name and class
template <typename F>
auto resolveSetting(std::string_view full_name, F && f)
{
if (full_name.starts_with(MERGE_TREE_SETTINGS_PREFIX))
{
std::string_view short_name = static_cast<std::string_view>(full_name).substr(MERGE_TREE_SETTINGS_PREFIX.size());
if (MergeTreeSettings::hasBuiltin(short_name)) // Check is required because `Settings` also contain names starting with 'merge_tree_' prefix
return f(short_name, SettingsType<MergeTreeSettings>());
}
// NOTE: other setting name resolution rules are to be added here
// If no rule works - use global namespace
return f(full_name, SettingsType<Settings>());
}
inline Field settingCastValueUtil(std::string_view full_name, const Field & value)
{
return resolveSetting(full_name, [&] <typename T> (std::string_view short_name, SettingsType<T>)
{
return T::castValueUtil(short_name, value);
});
}
inline String settingValueToStringUtil(std::string_view full_name, const Field & value)
{
return resolveSetting(full_name, [&] <typename T> (std::string_view short_name, SettingsType<T>)
{
return T::valueToStringUtil(short_name, value);
});
}
inline Field settingStringToValueUtil(std::string_view full_name, const String & str)
{
return resolveSetting(full_name, [&] <typename T> (std::string_view short_name, SettingsType<T>)
{
return T::stringToValueUtil(short_name, str);
});
}
inline bool settingIsBuiltin(std::string_view full_name)
{
return resolveSetting(full_name, [&] <typename T> (std::string_view short_name, SettingsType<T>)
{
return T::hasBuiltin(short_name);
});
}
template <typename T>
inline String settingFullName(std::string_view short_name);
template <>
inline String settingFullName<Settings>(std::string_view short_name)
{
return String(short_name);
}
template <>
inline String settingFullName<MergeTreeSettings>(std::string_view short_name)
{
String full_name(MERGE_TREE_SETTINGS_PREFIX);
full_name += short_name; // Just because you cannot concatenate `std::string_view` and `std::string` using operator+ in C++20 yet
return full_name;
}
inline std::string resolveSettingName(std::string_view full_name)
{
return resolveSetting(full_name, [&] <typename T> (std::string_view short_name, SettingsType<T>)
{
return settingFullName<T>(T::Traits::resolveName(short_name));
});
}
}
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