1 files changed, 3 insertions, 3 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index af37fcc1f1..09242a0f14 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -137,7 +137,7 @@ module ActiveRecord
       end
 
       def index_algorithms
-        { default: "ALGORITHM = DEFAULT".dup, copy: "ALGORITHM = COPY".dup, inplace: "ALGORITHM = INPLACE".dup }
+        { default: +"ALGORITHM = DEFAULT", copy: +"ALGORITHM = COPY", inplace: +"ALGORITHM = INPLACE" }
       end
 
       # HELPER METHODS ===========================================
@@ -392,7 +392,7 @@ module ActiveRecord
 
       def add_index(table_name, column_name, options = {}) #:nodoc:
         index_name, index_type, index_columns, _, index_algorithm, index_using, comment = add_index_options(table_name, column_name, options)
-        sql = "CREATE #{index_type} INDEX #{quote_column_name(index_name)} #{index_using} ON #{quote_table_name(table_name)} (#{index_columns}) #{index_algorithm}".dup
+        sql = +"CREATE #{index_type} INDEX #{quote_column_name(index_name)} #{index_using} ON #{quote_table_name(table_name)} (#{index_columns}) #{index_algorithm}"
         execute add_sql_comment!(sql, comment)
       end
 
@@ -785,7 +785,7 @@ module ActiveRecord
           # https://dev.mysql.com/doc/refman/5.7/en/set-names.html
           # (trailing comma because variable_assignments will always have content)
           if @config[:encoding]
-            encoding = "NAMES #{@config[:encoding]}".dup
+            encoding = +"NAMES #{@config[:encoding]}"
             encoding << " COLLATE #{@config[:collation]}" if @config[:collation]
             encoding << ", "
           end