1 files changed, 20 insertions, 0 deletions
diff --git a/string.c b/string.c
index 2e5a955627..8a8a0d4e18 100644
--- a/string.c
+++ b/string.c
@@ -27,6 +27,7 @@
 
 VALUE rb_cString;
 
+#define STR_TMPLOCK FL_USER1
 #define STR_ASSOC   FL_USER3
 #define STR_NOCAPA  (ELTS_SHARED|STR_ASSOC)
 
@@ -462,6 +463,9 @@ static int
 str_independent(str)
     VALUE str;
 {
+    if (FL_TEST(str, STR_TMPLOCK)) {
+	rb_raise(rb_eRuntimeError, "can't modify string; temporarily locked");
+    }
     if (OBJ_FROZEN(str)) rb_error_frozen("string");
     if (!OBJ_TAINTED(str) && rb_safe_level() >= 4)
 	rb_raise(rb_eSecurityError, "Insecure: can't modify string");
@@ -633,6 +637,22 @@ rb_str_dup_frozen(str)
 }
 
 VALUE
+rb_str_locktmp(str)
+    VALUE str;
+{
+    FL_SET(str, STR_TMPLOCK);
+    return str;
+}
+
+VALUE
+rb_str_unlocktmp(str)
+    VALUE str;
+{
+    FL_UNSET(str, STR_TMPLOCK);
+    return str;
+}
+
+VALUE
 rb_str_resize(str, len)
     VALUE str;
     long len;