Accept thread_safe as a keyword argument

Preserve the positional argument while allowing callers to use the
clearer keyword form.

Author: nobu

lib/pstore.rb

@@ -367,12 +367,13 @@ class Error < StandardError
   #
   # A \PStore object is
   # {reentrant}[https://en.wikipedia.org/wiki/Reentrancy_(computing)].
-  # If argument +thread_safe+ is given as +true+,
+  # If argument or keyword argument +thread_safe+ is given as +true+,
   # the object is also thread-safe (at the cost of a small performance penalty):
   #
   #   store = PStore.new(path, true)
+  #   store = PStore.new(path, thread_safe: true)
   #
-  def initialize(file, thread_safe = false)
+  def initialize(file, _thread_safe = false, thread_safe: _thread_safe)
     dir = File::dirname(file)
     unless File::directory? dir
       raise PStore::Error, format("directory %s does not exist", dir)

test/test_pstore.rb

@@ -128,6 +128,13 @@ def test_thread_safe
     File.unlink(second_file) rescue nil
   end
 
+  def test_thread_safe_argument
+    assert_equal false, PStore.new(@pstore_file).instance_variable_get(:@thread_safe)
+    assert_equal true, PStore.new(@pstore_file, true).instance_variable_get(:@thread_safe)
+    assert_equal true, PStore.new(@pstore_file, thread_safe: true).instance_variable_get(:@thread_safe)
+    assert_equal false, PStore.new(@pstore_file, true, thread_safe: false).instance_variable_get(:@thread_safe)
+  end
+
   def test_nested_transaction_raises_error
     assert_raise(PStore::Error) do
       @pstore.transaction { @pstore.transaction { } }