From 6d8bf54c440fd38eb12b3780556d6f7b88beb1ba Mon Sep 17 00:00:00 2001
From: ko1 <ko1@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Mon, 7 Dec 2015 15:10:00 +0000
Subject: [PATCH] * string.c: introduce String#+@ and String#-@ to control  
 String mutability.   [Feature #11782]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52917 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 ChangeLog                |  6 ++++++
 string.c                 | 42 ++++++++++++++++++++++++++++++++++++++++
 test/ruby/test_string.rb | 18 +++++++++++++++++
 3 files changed, 66 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 6a77703461..b755a1df4d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Mon Dec  7 23:45:20 2015  Koichi Sasada  <ko1@atdot.net>
+
+	* string.c: introduce String#+@ and String#-@ to control
+	  String mutability.
+	  [Feature #11782]
+
 Mon Dec  7 23:39:49 2015  Ben Miller  <bjmllr@gmail.com>
 
 	* parse.y: add heredoc <<~ syntax.  [Feature #9098]
diff --git a/string.c b/string.c
index 6d283dd145..a9fb005367 100644
--- a/string.c
+++ b/string.c
@@ -2227,6 +2227,46 @@ rb_str_freeze(VALUE str)
     return rb_obj_freeze(str);
 }
 
+
+/*
+ * call-seq:
+ *   +str  -> str (mutable)
+ *
+ * If the string is frozen, then return duplicated mutable string.
+ *
+ * If the string is not frozen, then return the string itself.
+ */
+static VALUE
+str_uplus(VALUE str)
+{
+    if (OBJ_FROZEN(str)) {
+	return rb_str_dup(str);
+    }
+    else {
+	return str;
+    }
+}
+
+/*
+ * call-seq:
+ *   -str  -> str (frozen)
+ *
+ * If the string is frozen, then return the string itself.
+ *
+ * If the string is not frozen, then duplicate the string
+ * freeze it and return it.
+ */
+static VALUE
+str_uminus(VALUE str)
+{
+    if (OBJ_FROZEN(str)) {
+	return str;
+    }
+    else {
+	return rb_str_freeze(rb_str_dup(str));
+    }
+}
+
 RUBY_ALIAS_FUNCTION(rb_str_dup_frozen(VALUE str), rb_str_new_frozen, (str))
 #define rb_str_dup_frozen rb_str_new_frozen
 
@@ -9295,6 +9335,8 @@ Init_String(void)
     rb_define_method(rb_cString, "scrub", str_scrub, -1);
     rb_define_method(rb_cString, "scrub!", str_scrub_bang, -1);
     rb_define_method(rb_cString, "freeze", rb_str_freeze, 0);
+    rb_define_method(rb_cString, "+@", str_uplus, 0);
+    rb_define_method(rb_cString, "-@", str_uminus, 0);
 
     rb_define_method(rb_cString, "to_i", rb_str_to_i, -1);
     rb_define_method(rb_cString, "to_f", rb_str_to_f, 0);
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index 7627fe12dc..824c0e6b1c 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -2252,6 +2252,24 @@ class TestString < Test::Unit::TestCase
     end;
   end if [0].pack("l!").bytesize < [nil].pack("p").bytesize
   # enable only when string size range is smaller than memory space
+
+  def test_uplus_minus
+    str = "foo"
+    assert_equal(false, str.frozen?)
+    assert_equal(false, (+str).frozen?)
+    assert_equal(true,  (-str).frozen?)
+
+    assert_equal(str.object_id, (+str).object_id)
+    assert_not_equal(str.object_id, (-str).object_id)
+
+    str = "bar".freeze
+    assert_equal(true,  str.frozen?)
+    assert_equal(false, (+str).frozen?)
+    assert_equal(true,  (-str).frozen?)
+
+    assert_not_equal(str.object_id, (+str).object_id)
+    assert_equal(str.object_id, (-str).object_id)
+  end
 end
 
 class TestString2 < TestString