add File.path

mrblib/file.rb

@@ -170,4 +170,14 @@ class File < IO
     ext = fname.split('.').last
     ext.empty? ? '' : ".#{ext}"
   end
+
+  def self.path(filename)
+    if filename.kind_of?(String)
+      filename
+    elsif filename.respond_to?(:to_path)
+      filename.to_path
+    else
+      raise TypeError, "no implicit conversion of #{filename.class} into String"
+    end
+  end
 end

test/file.rb

@@ -106,3 +106,12 @@ assert('File.expand_path (with ENV)') do
 
   assert_equal "#{ENV['HOME']}/user", File.expand_path("user", ENV['HOME']), "relative with base_dir"
 end
+
+assert('File.path') do
+  assert_equal "", File.path("")
+  assert_equal "a/b/c", File.path("a/b/c")
+  assert_equal "a/../b/./c", File.path("a/../b/./c")
+  assert_raise(TypeError) { File.path(nil) }
+  assert_raise(TypeError) { File.path(123) }
+
+end