jruby · Apr 3, 2015 · Apr 3, 2015 · Apr 3, 2015 · Apr 3, 2015
diff --git a/core/src/main/java/org/jruby/RubyString.java b/core/src/main/java/org/jruby/RubyString.java
@@ -3274,10 +3274,12 @@ public IRubyObject getbyte(ThreadContext context, IRubyObject index) {
 
     @JRubyMethod
     public IRubyObject setbyte(ThreadContext context, IRubyObject index, IRubyObject val) {
-        modifyAndKeepCodeRange();
         int i = RubyNumeric.num2int(index);
         int b = RubyNumeric.num2int(val);
-        value.getUnsafeBytes()[checkIndexForRef(i, value.getRealSize())] = (byte)b;
+        int normalizedIndex = checkIndexForRef(i, value.getRealSize());
+
+        modify19();
+        value.getUnsafeBytes()[normalizedIndex] = (byte)b;
         return val;
     }
 

diff --git a/spec/tags/ruby/core/string/setbyte_tags.txt b/spec/tags/ruby/core/string/setbyte_tags.txt
diff --git a/spec/tags/ruby/core/string/to_c_tags.txt b/spec/tags/ruby/core/string/to_c_tags.txt
diff --git a/spec/tags/ruby/core/string/to_r_tags.txt b/spec/tags/ruby/core/string/to_r_tags.txt
diff --git a/spec/truffle/tags/core/string/setbyte_tags.txt b/spec/truffle/tags/core/string/setbyte_tags.txt
diff --git a/truffle/src/main/java/org/jruby/truffle/nodes/core/StringNodes.java b/truffle/src/main/java/org/jruby/truffle/nodes/core/StringNodes.java
@@ -1292,7 +1292,8 @@ public RubyString initialize(RubyString self, RubyString from) {
                         getContext().getCoreLibrary().frozenError(self.getLogicalClass().getName(), this));
             }
 
-            self.set(from.getBytes());
+            // TODO (nirvdrum 03-Apr-15): Rather than dup every time, we should do CoW on String mutations.
+            self.set(from.getBytes().dup());
             self.setCodeRange(from.getCodeRange());
 
             return self;
@@ -1824,10 +1825,14 @@ public SetByteNode(SetByteNode prev) {
         }
 
         @Specialization
-        public Object setByte(RubyString string, int index, Object value) {
-            notDesignedForCompilation();
+        public int setByte(RubyString string, int index, int value) {
+            final int normalizedIndex = StringNodesHelper.checkIndexForRef(string, index, this);
+
+            string.modify();
+            string.clearCodeRange();
+            string.getByteList().getUnsafeBytes()[normalizedIndex] = (byte) value;
 
-            throw new UnsupportedOperationException("getbyte not implemented");
+            return value;
         }
     }
 
@@ -2577,6 +2582,30 @@ public static int checkIndex(RubyString string, int index, RubyNode node) {
             return index;
         }
 
+        public static int checkIndexForRef(RubyString string, int index, RubyNode node) {
+            final int length = string.getByteList().getRealSize();
+
+            if (index >= length) {
+                CompilerDirectives.transferToInterpreter();
+
+                throw new RaiseException(
+                        node.getContext().getCoreLibrary().indexError(String.format("index %d out of string", index), node));
+            }
+
+            if (index < 0) {
+                if (-index > length) {
+                    CompilerDirectives.transferToInterpreter();
+
+                    throw new RaiseException(
+                            node.getContext().getCoreLibrary().indexError(String.format("index %d out of string", index), node));
+                }
+
+                index += length;
+            }
+
+            return index;
+        }
+
         @TruffleBoundary
         public static void replaceInternal(RubyString string, int start, int length, RubyString replacement) {
             StringSupport.replaceInternal19(start, length, string, replacement);