we don't need a separate implementation of plusAssign for strings after all

idea/src/jet/Library.jet

@@ -78,7 +78,6 @@ class String() : Comparable<String> {
   val length : Int
 
   fun plus(other : Any?) : String
-  fun plusAssign(other: Any?): String
 
   fun equals(other : Any?) : Boolean
   fun equalsIgnoreCase(other: String?) : Boolean

idea/src/org/jetbrains/jet/codegen/ExpressionCodegen.java

@@ -1268,14 +1268,8 @@ public class ExpressionCodegen extends JetVisitor {
             }
         }
         else {
-            if (callable instanceof IntrinsicMethod) {
+            final boolean keepReturnValue = !((FunctionDescriptor) op).getReturnType().equals(JetStandardClasses.getUnitType());
-                final IntrinsicMethod intrinsic = (IntrinsicMethod) callable;
+            callAugAssignMethod(expression, (CallableMethod) callable, lhsType, keepReturnValue);
-                intrinsic.generate(this, v, Type.VOID_TYPE, expression, Arrays.asList(lhs, expression.getRight()), false);
-            }
-            else {
-                final boolean keepReturnValue = !((FunctionDescriptor) op).getReturnType().equals(JetStandardClasses.getUnitType());
-                callAugAssignMethod(expression, (CallableMethod) callable, lhsType, keepReturnValue);
-            }
         }
     }
 

idea/src/org/jetbrains/jet/codegen/intrinsics/Concat.java

@@ -16,7 +16,13 @@ public class Concat implements IntrinsicMethod {
     @Override
     public StackValue generate(ExpressionCodegen codegen, InstructionAdapter v, Type expectedType, PsiElement element, List<JetExpression> arguments, boolean haveReceiver) {
         codegen.generateStringBuilderConstructor();
-        codegen.invokeAppend(arguments.get(0));
+        if (haveReceiver) {
+            v.swap();
+            codegen.invokeAppendMethod(codegen.expressionType(arguments.get(0)));
+        }
+        else {
+            codegen.invokeAppend(arguments.get(0));
+        }
         codegen.invokeAppend(arguments.get(1));
         v.invokevirtual(ExpressionCodegen.CLASS_STRING_BUILDER, "toString", "()Ljava/lang/String;");
         return StackValue.onStack(Type.getObjectType("java/lang/String"));

idea/src/org/jetbrains/jet/codegen/intrinsics/IntrinsicMethods.java

@@ -66,7 +66,6 @@ public class IntrinsicMethods {
         declareIntrinsicFunction("Boolean", "not", 0, new Not());
 
         declareIntrinsicFunction("String", "plus", 1, new Concat());
-        declareIntrinsicFunction("String", "plusAssign", 1, new PlusConcat());
 
         declareIntrinsicStringMethods();
     }

idea/src/org/jetbrains/jet/codegen/intrinsics/PlusConcat.java

@@ -1,30 +0,0 @@
-package org.jetbrains.jet.codegen.intrinsics;
-
-import com.intellij.psi.PsiElement;
-import org.jetbrains.jet.codegen.ExpressionCodegen;
-import org.jetbrains.jet.codegen.StackValue;
-import org.jetbrains.jet.lang.psi.JetExpression;
-import org.objectweb.asm.Type;
-import org.objectweb.asm.commons.InstructionAdapter;
-
-import java.util.List;
-
-/**
- * @author yole
- */
-public class PlusConcat implements IntrinsicMethod {
-    @Override
-    public StackValue generate(ExpressionCodegen codegen, InstructionAdapter v, Type expectedType, PsiElement element, List<JetExpression> arguments, boolean haveReceiver) {
-        final JetExpression lhs = arguments.get(0);
-        final Type lhsType = codegen.expressionType(lhs);
-        codegen.generateStringBuilderConstructor();                  // StringBuilder
-        StackValue value = codegen.generateIntermediateValue(lhs);   // StringBuilder receiver
-        value.dupReceiver(v, 1);                                     // receiver StringBuilder receiver
-        value.put(lhsType, v);                                       // receiver StringBuilder value
-        codegen.invokeAppendMethod(lhsType);                         // receiver StringBuilder
-        codegen.invokeAppend(arguments.get(1));                      // receiver StringBuilder
-        v.invokevirtual(ExpressionCodegen.CLASS_STRING_BUILDER, "toString", "()Ljava/lang/String;");
-        value.store(v);
-        return null;
-    }
-}