Enable frozen_string_literal in all files in arel

68 files changed, 69 insertions, 1 deletions

diff --git a/lib/arel/alias_predication.rb b/lib/arel/alias_predication.rb
index f42e9ee1a6..cb50fb95be 100644
--- a/lib/arel/alias_predication.rb
+++ b/lib/arel/alias_predication.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module AliasPredication
     def as other
diff --git a/lib/arel/attributes.rb b/lib/arel/attributes.rb
index 92cc041f83..ed4739ebed 100644
--- a/lib/arel/attributes.rb
+++ b/lib/arel/attributes.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'arel/attributes/attribute'
 
 module Arel
diff --git a/lib/arel/attributes/attribute.rb b/lib/arel/attributes/attribute.rb
index cda5a5a3db..41bc0c32c7 100644
--- a/lib/arel/attributes/attribute.rb
+++ b/lib/arel/attributes/attribute.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Attributes
     class Attribute < Struct.new :relation, :name
diff --git a/lib/arel/collectors/bind.rb b/lib/arel/collectors/bind.rb
index 05cd966509..dfa79d1001 100644
--- a/lib/arel/collectors/bind.rb
+++ b/lib/arel/collectors/bind.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Collectors
     class Bind
diff --git a/lib/arel/collectors/plain_string.rb b/lib/arel/collectors/plain_string.rb
index 2505bc376e..1e8d2a2152 100644
--- a/lib/arel/collectors/plain_string.rb
+++ b/lib/arel/collectors/plain_string.rb
@@ -1,8 +1,9 @@
+# frozen_string_literal: true
 module Arel
   module Collectors
     class PlainString
       def initialize
-        @str = ''
+        @str = ''.dup
       end
 
       def value
diff --git a/lib/arel/collectors/sql_string.rb b/lib/arel/collectors/sql_string.rb
index fd2faaef3a..5f42117331 100644
--- a/lib/arel/collectors/sql_string.rb
+++ b/lib/arel/collectors/sql_string.rb
@@ -1,4 +1,5 @@
 # encoding: utf-8
+# frozen_string_literal: true
 
 require 'arel/collectors/plain_string'
 
diff --git a/lib/arel/compatibility/wheres.rb b/lib/arel/compatibility/wheres.rb
index b73b178651..3e60894bd8 100644
--- a/lib/arel/compatibility/wheres.rb
+++ b/lib/arel/compatibility/wheres.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Compatibility # :nodoc:
     class Wheres # :nodoc:
diff --git a/lib/arel/crud.rb b/lib/arel/crud.rb
index d310c7381f..2d10432205 100644
--- a/lib/arel/crud.rb
+++ b/lib/arel/crud.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   ###
   # FIXME hopefully we can remove this
diff --git a/lib/arel/delete_manager.rb b/lib/arel/delete_manager.rb
index 20e988e01f..aee4511249 100644
--- a/lib/arel/delete_manager.rb
+++ b/lib/arel/delete_manager.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   class DeleteManager < Arel::TreeManager
     def initialize
diff --git a/lib/arel/errors.rb b/lib/arel/errors.rb
index c8a6af9f77..86fbb80461 100644
--- a/lib/arel/errors.rb
+++ b/lib/arel/errors.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   class ArelError < StandardError
   end
diff --git a/lib/arel/expressions.rb b/lib/arel/expressions.rb
index d40268c292..612a0942f1 100644
--- a/lib/arel/expressions.rb
+++ b/lib/arel/expressions.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Expressions
     def count distinct = false
diff --git a/lib/arel/factory_methods.rb b/lib/arel/factory_methods.rb
index cb66f6f888..6647c5ac44 100644
--- a/lib/arel/factory_methods.rb
+++ b/lib/arel/factory_methods.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   ###
   # Methods for creating various nodes
diff --git a/lib/arel/insert_manager.rb b/lib/arel/insert_manager.rb
index 7829c3f4f9..d0a49842de 100644
--- a/lib/arel/insert_manager.rb
+++ b/lib/arel/insert_manager.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   class InsertManager < Arel::TreeManager
     def initialize
diff --git a/lib/arel/math.rb b/lib/arel/math.rb
index 04cae84598..9e6549b58f 100644
--- a/lib/arel/math.rb
+++ b/lib/arel/math.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Math
     def *(other)
diff --git a/lib/arel/nodes.rb b/lib/arel/nodes.rb
index ff27bb9aa8..8c9815a96b 100644
--- a/lib/arel/nodes.rb
+++ b/lib/arel/nodes.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # node
 require 'arel/nodes/node'
 require 'arel/nodes/select_statement'
diff --git a/lib/arel/nodes/and.rb b/lib/arel/nodes/and.rb
index 8e1afda709..1e2f61cf43 100644
--- a/lib/arel/nodes/and.rb
+++ b/lib/arel/nodes/and.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class And < Arel::Nodes::Node
diff --git a/lib/arel/nodes/ascending.rb b/lib/arel/nodes/ascending.rb
index bca00a8339..adadab55e4 100644
--- a/lib/arel/nodes/ascending.rb
+++ b/lib/arel/nodes/ascending.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Ascending < Ordering
diff --git a/lib/arel/nodes/binary.rb b/lib/arel/nodes/binary.rb
index 763091c267..3001788774 100644
--- a/lib/arel/nodes/binary.rb
+++ b/lib/arel/nodes/binary.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Binary < Arel::Nodes::Node
diff --git a/lib/arel/nodes/bind_param.rb b/lib/arel/nodes/bind_param.rb
index 3a4aedc4ba..9e297831cd 100644
--- a/lib/arel/nodes/bind_param.rb
+++ b/lib/arel/nodes/bind_param.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class BindParam < Node
diff --git a/lib/arel/nodes/case.rb b/lib/arel/nodes/case.rb
index 85f8851dbe..1edca40001 100644
--- a/lib/arel/nodes/case.rb
+++ b/lib/arel/nodes/case.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Case < Arel::Nodes::Node
diff --git a/lib/arel/nodes/casted.rb b/lib/arel/nodes/casted.rb
index 6b15f9e4b3..290e4dd38c 100644
--- a/lib/arel/nodes/casted.rb
+++ b/lib/arel/nodes/casted.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Casted < Arel::Nodes::Node # :nodoc:
diff --git a/lib/arel/nodes/count.rb b/lib/arel/nodes/count.rb
index 5c8ade1cf9..a7c6236a22 100644
--- a/lib/arel/nodes/count.rb
+++ b/lib/arel/nodes/count.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Count < Arel::Nodes::Function
diff --git a/lib/arel/nodes/delete_statement.rb b/lib/arel/nodes/delete_statement.rb
index 8aaf8ca0b6..593ce9bddf 100644
--- a/lib/arel/nodes/delete_statement.rb
+++ b/lib/arel/nodes/delete_statement.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class DeleteStatement < Arel::Nodes::Binary
diff --git a/lib/arel/nodes/descending.rb b/lib/arel/nodes/descending.rb
index d886bdcb5f..d7261ab583 100644
--- a/lib/arel/nodes/descending.rb
+++ b/lib/arel/nodes/descending.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Descending < Ordering
diff --git a/lib/arel/nodes/equality.rb b/lib/arel/nodes/equality.rb
index f29344e580..ef44725e24 100644
--- a/lib/arel/nodes/equality.rb
+++ b/lib/arel/nodes/equality.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Equality < Arel::Nodes::Binary
diff --git a/lib/arel/nodes/extract.rb b/lib/arel/nodes/extract.rb
index 7ed678ca08..4e797b6770 100644
--- a/lib/arel/nodes/extract.rb
+++ b/lib/arel/nodes/extract.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Extract < Arel::Nodes::Unary
diff --git a/lib/arel/nodes/false.rb b/lib/arel/nodes/false.rb
index 6df70e43ce..26b4e5db97 100644
--- a/lib/arel/nodes/false.rb
+++ b/lib/arel/nodes/false.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class False < Arel::Nodes::Node
diff --git a/lib/arel/nodes/full_outer_join.rb b/lib/arel/nodes/full_outer_join.rb
index 708f161c9a..12a02d8cd9 100644
--- a/lib/arel/nodes/full_outer_join.rb
+++ b/lib/arel/nodes/full_outer_join.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class FullOuterJoin < Arel::Nodes::Join
diff --git a/lib/arel/nodes/function.rb b/lib/arel/nodes/function.rb
index 182dfa7329..28a394e9f3 100644
--- a/lib/arel/nodes/function.rb
+++ b/lib/arel/nodes/function.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Function < Arel::Nodes::Node
diff --git a/lib/arel/nodes/grouping.rb b/lib/arel/nodes/grouping.rb
index e7f4bd9cd5..16911eb3b6 100644
--- a/lib/arel/nodes/grouping.rb
+++ b/lib/arel/nodes/grouping.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Grouping < Unary
diff --git a/lib/arel/nodes/in.rb b/lib/arel/nodes/in.rb
index 6ccf37a053..30cd771c40 100644
--- a/lib/arel/nodes/in.rb
+++ b/lib/arel/nodes/in.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class In < Equality
diff --git a/lib/arel/nodes/infix_operation.rb b/lib/arel/nodes/infix_operation.rb
index 55ac715f73..4eb7c5356f 100644
--- a/lib/arel/nodes/infix_operation.rb
+++ b/lib/arel/nodes/infix_operation.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
 
diff --git a/lib/arel/nodes/inner_join.rb b/lib/arel/nodes/inner_join.rb
index bf10eeac18..4e398267c3 100644
--- a/lib/arel/nodes/inner_join.rb
+++ b/lib/arel/nodes/inner_join.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class InnerJoin < Arel::Nodes::Join
diff --git a/lib/arel/nodes/insert_statement.rb b/lib/arel/nodes/insert_statement.rb
index ada4fcc562..72793bc1ad 100644
--- a/lib/arel/nodes/insert_statement.rb
+++ b/lib/arel/nodes/insert_statement.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class InsertStatement < Arel::Nodes::Node
diff --git a/lib/arel/nodes/join_source.rb b/lib/arel/nodes/join_source.rb
index da828cf9ee..428ce8183e 100644
--- a/lib/arel/nodes/join_source.rb
+++ b/lib/arel/nodes/join_source.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     ###
diff --git a/lib/arel/nodes/matches.rb b/lib/arel/nodes/matches.rb
index 0d9c1925dc..3ad3850a8e 100644
--- a/lib/arel/nodes/matches.rb
+++ b/lib/arel/nodes/matches.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Matches < Binary
diff --git a/lib/arel/nodes/named_function.rb b/lib/arel/nodes/named_function.rb
index c792f0af98..173838a7fd 100644
--- a/lib/arel/nodes/named_function.rb
+++ b/lib/arel/nodes/named_function.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class NamedFunction < Arel::Nodes::Function
diff --git a/lib/arel/nodes/node.rb b/lib/arel/nodes/node.rb
index 239c4fd766..34e71063af 100644
--- a/lib/arel/nodes/node.rb
+++ b/lib/arel/nodes/node.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'arel/collectors/sql_string'
 
 module Arel
diff --git a/lib/arel/nodes/outer_join.rb b/lib/arel/nodes/outer_join.rb
index bea5578b95..c568655fe6 100644
--- a/lib/arel/nodes/outer_join.rb
+++ b/lib/arel/nodes/outer_join.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class OuterJoin < Arel::Nodes::Join
diff --git a/lib/arel/nodes/over.rb b/lib/arel/nodes/over.rb
index 21d1b5029e..47a34e69ea 100644
--- a/lib/arel/nodes/over.rb
+++ b/lib/arel/nodes/over.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
 
diff --git a/lib/arel/nodes/regexp.rb b/lib/arel/nodes/regexp.rb
index 784368f5bf..8a76185ef0 100644
--- a/lib/arel/nodes/regexp.rb
+++ b/lib/arel/nodes/regexp.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Regexp < Binary
diff --git a/lib/arel/nodes/right_outer_join.rb b/lib/arel/nodes/right_outer_join.rb
index ea1ddb7d52..04ab31ebf0 100644
--- a/lib/arel/nodes/right_outer_join.rb
+++ b/lib/arel/nodes/right_outer_join.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class RightOuterJoin < Arel::Nodes::Join
diff --git a/lib/arel/nodes/select_core.rb b/lib/arel/nodes/select_core.rb
index 3696dd20af..264fa46591 100644
--- a/lib/arel/nodes/select_core.rb
+++ b/lib/arel/nodes/select_core.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class SelectCore < Arel::Nodes::Node
diff --git a/lib/arel/nodes/select_statement.rb b/lib/arel/nodes/select_statement.rb
index 830ac27046..641a08405d 100644
--- a/lib/arel/nodes/select_statement.rb
+++ b/lib/arel/nodes/select_statement.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class SelectStatement < Arel::Nodes::Node
diff --git a/lib/arel/nodes/sql_literal.rb b/lib/arel/nodes/sql_literal.rb
index 2c56644b99..73575a7d49 100644
--- a/lib/arel/nodes/sql_literal.rb
+++ b/lib/arel/nodes/sql_literal.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class SqlLiteral < String
diff --git a/lib/arel/nodes/string_join.rb b/lib/arel/nodes/string_join.rb
index 7fb0033c0f..21d6845c45 100644
--- a/lib/arel/nodes/string_join.rb
+++ b/lib/arel/nodes/string_join.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class StringJoin < Arel::Nodes::Join
diff --git a/lib/arel/nodes/table_alias.rb b/lib/arel/nodes/table_alias.rb
index a5adc0766a..78deb175b6 100644
--- a/lib/arel/nodes/table_alias.rb
+++ b/lib/arel/nodes/table_alias.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class TableAlias < Arel::Nodes::Binary
diff --git a/lib/arel/nodes/terminal.rb b/lib/arel/nodes/terminal.rb
index f4cdfdfe17..6f60fe006f 100644
--- a/lib/arel/nodes/terminal.rb
+++ b/lib/arel/nodes/terminal.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Distinct < Arel::Nodes::Node
diff --git a/lib/arel/nodes/true.rb b/lib/arel/nodes/true.rb
index 082963e5e6..796b5b9348 100644
--- a/lib/arel/nodes/true.rb
+++ b/lib/arel/nodes/true.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class True < Arel::Nodes::Node
diff --git a/lib/arel/nodes/unary.rb b/lib/arel/nodes/unary.rb
index 50946980b4..a42744b1d5 100644
--- a/lib/arel/nodes/unary.rb
+++ b/lib/arel/nodes/unary.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Unary < Arel::Nodes::Node
diff --git a/lib/arel/nodes/unary_operation.rb b/lib/arel/nodes/unary_operation.rb
index 1636c01279..3c56ef2026 100644
--- a/lib/arel/nodes/unary_operation.rb
+++ b/lib/arel/nodes/unary_operation.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
 
diff --git a/lib/arel/nodes/unqualified_column.rb b/lib/arel/nodes/unqualified_column.rb
index 2820dba9d2..f9017238c8 100644
--- a/lib/arel/nodes/unqualified_column.rb
+++ b/lib/arel/nodes/unqualified_column.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class UnqualifiedColumn < Arel::Nodes::Unary
diff --git a/lib/arel/nodes/update_statement.rb b/lib/arel/nodes/update_statement.rb
index d6831dc242..286f0bd3ce 100644
--- a/lib/arel/nodes/update_statement.rb
+++ b/lib/arel/nodes/update_statement.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class UpdateStatement < Arel::Nodes::Node
diff --git a/lib/arel/nodes/values.rb b/lib/arel/nodes/values.rb
index 814e843dab..b32d5063a2 100644
--- a/lib/arel/nodes/values.rb
+++ b/lib/arel/nodes/values.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Values < Arel::Nodes::Binary
diff --git a/lib/arel/nodes/window.rb b/lib/arel/nodes/window.rb
index fee8eeff7a..535c0c6238 100644
--- a/lib/arel/nodes/window.rb
+++ b/lib/arel/nodes/window.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class Window < Arel::Nodes::Node
diff --git a/lib/arel/nodes/with.rb b/lib/arel/nodes/with.rb
index 7f08abe47d..def7840ea3 100644
--- a/lib/arel/nodes/with.rb
+++ b/lib/arel/nodes/with.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Nodes
     class With < Arel::Nodes::Unary
diff --git a/lib/arel/order_predications.rb b/lib/arel/order_predications.rb
index 153fcffb41..d84be82bb6 100644
--- a/lib/arel/order_predications.rb
+++ b/lib/arel/order_predications.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module OrderPredications
 
diff --git a/lib/arel/predications.rb b/lib/arel/predications.rb
index 81bf3b4d95..799c7c67b8 100644
--- a/lib/arel/predications.rb
+++ b/lib/arel/predications.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Predications
     def not_eq other
diff --git a/lib/arel/select_manager.rb b/lib/arel/select_manager.rb
index 6af9b6fbe6..0b35176842 100644
--- a/lib/arel/select_manager.rb
+++ b/lib/arel/select_manager.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'arel/collectors/sql_string'
 
 module Arel
diff --git a/lib/arel/table.rb b/lib/arel/table.rb
index 130b7ea028..b3f2d79e5f 100644
--- a/lib/arel/table.rb
+++ b/lib/arel/table.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   class Table
     include Arel::Crud
diff --git a/lib/arel/tree_manager.rb b/lib/arel/tree_manager.rb
index 5278ab06a1..cc3f1eeee4 100644
--- a/lib/arel/tree_manager.rb
+++ b/lib/arel/tree_manager.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'arel/collectors/sql_string'
 
 module Arel
diff --git a/lib/arel/update_manager.rb b/lib/arel/update_manager.rb
index 36fb74fe7c..eac414eafb 100644
--- a/lib/arel/update_manager.rb
+++ b/lib/arel/update_manager.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   class UpdateManager < Arel::TreeManager
     def initialize
diff --git a/lib/arel/visitors.rb b/lib/arel/visitors.rb
index 9bf5170463..a3404cf992 100644
--- a/lib/arel/visitors.rb
+++ b/lib/arel/visitors.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'arel/visitors/visitor'
 require 'arel/visitors/depth_first'
 require 'arel/visitors/to_sql'
diff --git a/lib/arel/visitors/bind_substitute.rb b/lib/arel/visitors/bind_substitute.rb
index ce0fb5c924..52c96b0d72 100644
--- a/lib/arel/visitors/bind_substitute.rb
+++ b/lib/arel/visitors/bind_substitute.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Visitors
     class BindSubstitute
diff --git a/lib/arel/visitors/depth_first.rb b/lib/arel/visitors/depth_first.rb
index 69ed345aea..5416a285f5 100644
--- a/lib/arel/visitors/depth_first.rb
+++ b/lib/arel/visitors/depth_first.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Visitors
     class DepthFirst < Arel::Visitors::Visitor
diff --git a/lib/arel/visitors/reduce.rb b/lib/arel/visitors/reduce.rb
index 9670cad27c..7948758e2f 100644
--- a/lib/arel/visitors/reduce.rb
+++ b/lib/arel/visitors/reduce.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'arel/visitors/visitor'
 
 module Arel
diff --git a/lib/arel/visitors/visitor.rb b/lib/arel/visitors/visitor.rb
index bfe7342f04..b96b8238a7 100644
--- a/lib/arel/visitors/visitor.rb
+++ b/lib/arel/visitors/visitor.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module Visitors
     class Visitor
diff --git a/lib/arel/window_predications.rb b/lib/arel/window_predications.rb
index 71844eab53..f93dede036 100644
--- a/lib/arel/window_predications.rb
+++ b/lib/arel/window_predications.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Arel
   module WindowPredications