diff --git a/src/ameba/runner.cr b/src/ameba/runner.cr
index dd2ca2f7..87e398c6 100644
--- a/src/ameba/runner.cr
+++ b/src/ameba/runner.cr
@@ -19,8 +19,7 @@ module Ameba
       def initialize(path, issues_by_iteration, loop_start = -1)
         root_cause =
           issues_by_iteration[loop_start..-1]
-            .map(&.map(&.rule.name).uniq!.join(", "))
-            .join(" -> ")
+            .join(" -> ", &.map(&.rule.name).uniq!.join(", "))
 
         message = String.build do |io|
           io << "Infinite loop"
@@ -210,7 +209,7 @@ module Ameba
     private def check_for_infinite_loop(source, corrected_issues, processed_sources)
       checksum = Digest::SHA1.hexdigest(source.code)
 
-      if (loop_start = processed_sources.index(checksum))
+      if loop_start = processed_sources.index(checksum)
         raise InfiniteCorrectionLoopError.new(
           source.path,
           corrected_issues,
diff --git a/src/ameba/source.cr b/src/ameba/source.cr
index 8e27c242..d6e0b97d 100644
--- a/src/ameba/source.cr
+++ b/src/ameba/source.cr
@@ -11,9 +11,6 @@ module Ameba
     # Crystal code (content of a source file).
     getter code : String
 
-    @lines : Array(String)?
-    @ast : Crystal::ASTNode?
-
     # Creates a new source by `code` and `path`.
     #
     # For example:
@@ -50,9 +47,7 @@ module Ameba
     # source.lines # => ["a = 1", "b = 2"]
     # ```
     #
-    def lines : Array(String)
-      @lines ||= code.split('\n')
-    end
+    getter lines : Array(String) { code.split('\n') }
 
     # Returns AST nodes constructed by `Crystal::Parser`.
     #
@@ -61,12 +56,11 @@ module Ameba
     # source.ast
     # ```
     #
-    def ast : Crystal::ASTNode
-      @ast ||=
-        Crystal::Parser.new(code)
-          .tap(&.wants_doc = true)
-          .tap(&.filename = path)
-          .parse
+    getter ast : Crystal::ASTNode do
+      Crystal::Parser.new(code)
+        .tap(&.wants_doc = true)
+        .tap(&.filename = path)
+        .parse
     end
 
     getter fullpath : String do
diff --git a/src/ameba/source/corrector.cr b/src/ameba/source/corrector.cr
index 43b3d348..94124786 100644
--- a/src/ameba/source/corrector.cr
+++ b/src/ameba/source/corrector.cr
@@ -8,7 +8,7 @@ class Ameba::Source
 
     def initialize(code : String)
       @rewriter = Rewriter.new(code)
-      @line_sizes = code.lines(chomp: false).map(&.size)
+      @line_sizes = code.each_line(chomp: false).map(&.size).to_a
     end
 
     # Replaces the code of the given range with *content*.
diff --git a/src/ameba/source/rewriter.cr b/src/ameba/source/rewriter.cr
index 6825ea87..5eda2d6a 100644
--- a/src/ameba/source/rewriter.cr
+++ b/src/ameba/source/rewriter.cr
@@ -59,9 +59,9 @@ class Ameba::Source
   # The updates are organized in a tree, according to the ranges they act on
   # (where children are strictly contained by their parent).
   class Rewriter
-    getter code
+    getter code : String
 
-    def initialize(@code : String)
+    def initialize(@code)
       @action_root = Rewriter::Action.new(0, code.size)
     end
 
diff --git a/src/ameba/source/rewriter/action.cr b/src/ameba/source/rewriter/action.cr
index df4d1270..456ad33a 100644
--- a/src/ameba/source/rewriter/action.cr
+++ b/src/ameba/source/rewriter/action.cr
@@ -73,21 +73,23 @@ class Ameba::Source::Rewriter
       family = analyse_hierarchy(action)
       sibling_left, sibling_right = family[:sibling_left], family[:sibling_right]
 
-      if (fusible = family[:fusible])
+      if fusible = family[:fusible]
         child = family[:child]
         child ||= [] of Action
         fuse_deletions(action, fusible, sibling_left + child + sibling_right)
       else
-        extra_sibling = if (parent = family[:parent])
-                          # action should be a descendant of one of the children
-                          parent.do_combine(action)
-                        elsif (child = family[:child])
-                          # or it should become the parent of some of the children,
-                          action.with(children: child).combine_children(action.children)
-                        else
-                          # or else it should become an additional child
-                          action
-                        end
+        extra_sibling =
+          case
+          when parent = family[:parent]
+            # action should be a descendant of one of the children
+            parent.do_combine(action)
+          when child = family[:child]
+            # or it should become the parent of some of the children,
+            action.with(children: child).combine_children(action.children)
+          else
+            # or else it should become an additional child
+            action
+          end
         self.with(children: sibling_left + [extra_sibling] + sibling_right)
       end
     end
@@ -102,8 +104,8 @@ class Ameba::Source::Rewriter
     protected def fuse_deletions(action, fusible, other_siblings)
       without_fusible = self.with(children: other_siblings)
       fusible = [action] + fusible
-      fused_begin_pos = fusible.map(&.begin_pos).min
-      fused_end_pos = fusible.map(&.end_pos).max
+      fused_begin_pos = fusible.min_of(&.begin_pos)
+      fused_end_pos = fusible.max_of(&.end_pos)
       fused_deletion = action.with(begin_pos: fused_begin_pos, end_pos: fused_end_pos)
       without_fusible.do_combine(fused_deletion)
     end