Make SettingsChanges a class.

src/Access/EnabledSettings.cpp

 #include <Access/EnabledSettings.h>
+#include <Common/SettingsChanges.h>
 
 
 namespace DB

src/Access/EnabledSettings.h

@@ -2,7 +2,6 @@
 
 #include <Core/Types.h>
 #include <Core/UUID.h>
-#include <Common/SettingsChanges.h>
 #include <Access/SettingsConstraints.h>
 #include <Access/SettingsProfileElement.h>
 #include <boost/container/flat_set.hpp>

src/Access/SettingsConstraints.cpp

 #include <Access/SettingsConstraints.h>
 #include <Core/Settings.h>
 #include <Common/FieldVisitors.h>
+#include <Common/SettingsChanges.h>
 #include <IO/WriteHelpers.h>
 #include <Poco/Util/AbstractConfiguration.h>
 

src/Access/SettingsConstraints.h

 #pragma once
 
 #include <Core/Field.h>
-#include <Common/SettingsChanges.h>
 #include <common/StringRef.h>
 #include <unordered_map>
 
@@ -18,6 +17,8 @@ namespace Util
 namespace DB
 {
 struct Settings;
+struct SettingChange;
+class SettingsChanges;
 
 /** Checks if specified changes of settings are allowed or not.
   * If the changes are not allowed (i.e. violates some constraints) this class throws an exception.

src/Access/SettingsProfileElement.cpp

@@ -4,6 +4,7 @@
 #include <Access/SettingsProfile.h>
 #include <Parsers/ASTSettingsProfileElement.h>
 #include <Core/Settings.h>
+#include <Common/SettingsChanges.h>
 #include <IO/ReadHelpers.h>
 #include <IO/WriteHelpers.h>
 

src/Access/SettingsProfileElement.h

@@ -9,8 +9,7 @@
 namespace DB
 {
 struct Settings;
-struct SettingChange;
-using SettingsChanges = std::vector<SettingChange>;
+class SettingsChanges;
 class SettingsConstraints;
 class ASTSettingsProfileElement;
 class ASTSettingsProfileElements;

src/Access/SettingsProfilesCache.cpp

@@ -2,6 +2,7 @@
 #include <Access/AccessControlManager.h>
 #include <Access/SettingsProfile.h>
 #include <Core/Settings.h>
+#include <Common/SettingsChanges.h>
 #include <Common/quoteString.h>
 #include <boost/range/adaptor/map.hpp>
 #include <boost/range/algorithm_ext/push_back.hpp>

src/Common/SettingsChanges.cpp

+#include <Common/SettingsChanges.h>
+
+
+namespace DB
+{
+namespace
+{
+    SettingChange * find(SettingsChanges & changes, const std::string_view & name)
+    {
+        auto it = std::find_if(changes.begin(), changes.end(), [&name](const SettingChange & change) { return change.name == name; });
+        if (it == changes.end())
+            return nullptr;
+        return &*it;
+    }
+
+    const SettingChange * find(const SettingsChanges & changes, const std::string_view & name)
+    {
+        auto it = std::find_if(changes.begin(), changes.end(), [&name](const SettingChange & change) { return change.name == name; });
+        if (it == changes.end())
+            return nullptr;
+        return &*it;
+    }
+}
+
+bool SettingsChanges::tryGet(const std::string_view & name, Field & out_value) const
+{
+    const auto * change = find(*this, name);
+    if (!change)
+        return false;
+    out_value = change->value;
+    return true;
+}
+
+const Field * SettingsChanges::tryGet(const std::string_view & name) const
+{
+    const auto * change = find(*this, name);
+    if (!change)
+        return nullptr;
+    return &change->value;
+}
+
+Field * SettingsChanges::tryGet(const std::string_view & name)
+{
+    auto * change = find(*this, name);
+    if (!change)
+        return nullptr;
+    return &change->value;
+}
+
+}

src/Common/SettingsChanges.h

@@ -5,21 +5,28 @@
 
 namespace DB
 {
-
 struct SettingChange
 {
     String name;
     Field value;
-    SettingChange() {}
 
-    SettingChange(const String & name_, const Field value_)
-    : name(name_)
-    , value(value_) {}
+    SettingChange() {}
+    SettingChange(const std::string_view & name_, const Field & value_) : name(name_), value(value_) {}
+    SettingChange(const std::string_view & name_, Field && value_) : name(name_), value(std::move(value_)) {}
 
     friend bool operator ==(const SettingChange & lhs, const SettingChange & rhs) { return (lhs.name == rhs.name) && (lhs.value == rhs.value); }
     friend bool operator !=(const SettingChange & lhs, const SettingChange & rhs) { return !(lhs == rhs); }
 };
 
-using SettingsChanges = std::vector<SettingChange>;
+
+class SettingsChanges : public std::vector<SettingChange>
+{
+public:
+    using std::vector<SettingChange>::vector;
+
+    bool tryGet(const std::string_view & name, Field & out_value) const;
+    const Field * tryGet(const std::string_view & name) const;
+    Field * tryGet(const std::string_view & name);
+};
 
 }

src/Common/ya.make

@@ -75,6 +75,7 @@ SRCS(
     RWLock.cpp
     SensitiveDataMasker.cpp
     setThreadName.cpp
+    SettingsChanges.cpp
     SharedLibrary.cpp
     ShellCommand.cpp
     StackTrace.cpp

src/Core/SettingsCollection.h

@@ -14,7 +14,7 @@ namespace DB
 
 class Field;
 struct SettingChange;
-using SettingsChanges = std::vector<SettingChange>;
+class SettingsChanges;
 class ReadBuffer;
 class WriteBuffer;
 enum class SettingsBinaryFormat;

src/Parsers/QueryWithOutputSettingsPushDownVisitor.h

@@ -8,7 +8,7 @@ namespace DB
 
 class ASTSelectQuery;
 struct SettingChange;
-using SettingsChanges = std::vector<SettingChange>;
+class SettingsChanges;
 
 /// Pushdown SETTINGS clause that goes after FORMAT to the SELECT query:
 /// (since settings after FORMAT parsed separatelly not in the ParserSelectQuery but in ParserQueryWithOutput)

src/Storages/IStorage.h

@@ -37,8 +37,6 @@ using StorageActionBlockType = size_t;
 class ASTCreateQuery;
 
 struct Settings;
-struct SettingChange;
-using SettingsChanges = std::vector<SettingChange>;
 
 class AlterCommands;
 class MutationCommands;

src/Storages/Kafka/StorageKafka.h

@@ -5,6 +5,7 @@
 #include <Storages/Kafka/Buffer_fwd.h>
 #include <Storages/Kafka/KafkaSettings.h>
 #include <Interpreters/Context.h>
+#include <Common/SettingsChanges.h>
 
 #include <Poco/Semaphore.h>
 #include <ext/shared_ptr_helper.h>

src/Storages/MergeTree/MergeTreeData.cpp

@@ -1472,24 +1472,22 @@ void MergeTreeData::checkAlterIsPossible(const AlterCommands & commands, const S
         const auto & new_changes = new_metadata.settings_changes->as<const ASTSetQuery &>().changes;
         for (const auto & changed_setting : new_changes)
         {
-            if (MergeTreeSettings::findIndex(changed_setting.name) == MergeTreeSettings::npos)
-                throw Exception{"Storage '" + getName() + "' doesn't have setting '" + changed_setting.name + "'",
+            const auto & setting_name = changed_setting.name;
+            const auto & new_value = changed_setting.value;
+            if (MergeTreeSettings::findIndex(setting_name) == MergeTreeSettings::npos)
+                throw Exception{"Storage '" + getName() + "' doesn't have setting '" + setting_name + "'",
                                 ErrorCodes::UNKNOWN_SETTING};
 
-            auto comparator = [&changed_setting](const auto & change) { return change.name == changed_setting.name; };
+            const Field * current_value = current_changes.tryGet(setting_name);
 
-            auto current_setting_it
-                = std::find_if(current_changes.begin(), current_changes.end(), comparator);
-
-            if ((current_setting_it == current_changes.end() || *current_setting_it != changed_setting)
-                && MergeTreeSettings::isReadonlySetting(changed_setting.name))
+            if ((!current_value || *current_value != new_value)
+                && MergeTreeSettings::isReadonlySetting(setting_name))
             {
-                throw Exception{"Setting '" + changed_setting.name + "' is readonly for storage '" + getName() + "'",
+                throw Exception{"Setting '" + setting_name + "' is readonly for storage '" + getName() + "'",
                                  ErrorCodes::READONLY_SETTING};
             }
 
-            if (current_setting_it == current_changes.end()
-                && MergeTreeSettings::isPartFormatSetting(changed_setting.name))
+            if (!current_value && MergeTreeSettings::isPartFormatSetting(setting_name))
             {
                 MergeTreeSettings copy = *getSettings();
                 copy.applyChange(changed_setting);
@@ -1498,8 +1496,8 @@ void MergeTreeData::checkAlterIsPossible(const AlterCommands & commands, const S
                     throw Exception("Can't change settings. Reason: " + reason, ErrorCodes::NOT_IMPLEMENTED);
             }
 
-            if (changed_setting.name == "storage_policy")
-                checkStoragePolicy(global_context.getStoragePolicy(changed_setting.value.safeGet<String>()));
+            if (setting_name == "storage_policy")
+                checkStoragePolicy(global_context.getStoragePolicy(new_value.safeGet<String>()));
         }
     }
 

src/Storages/MergeTree/MergeTreeSettings.h

@@ -2,7 +2,6 @@
 
 #include <Core/Defines.h>
 #include <Core/SettingsCollection.h>
-#include <Common/SettingsChanges.h>
 
 
 namespace Poco