fun String?.plus(other: Any?) : String

compiler/backend/src/org/jetbrains/jet/codegen/intrinsics/IntrinsicMethods.java

@@ -75,6 +75,7 @@ public class IntrinsicMethods {
 
         declareOverload(myStdLib.getLibraryScope().getFunctions("toString"), 0, new ToString());
         declareOverload(myStdLib.getLibraryScope().getFunctions("equals"), 1, new Equals());
+        declareOverload(myStdLib.getLibraryScope().getFunctions("plus"), 1, new StringPlus());
 
 //        declareIntrinsicFunction("Any", "equals", 1, new Equals());
 //

compiler/backend/src/org/jetbrains/jet/codegen/intrinsics/StringPlus.java

@@ -0,0 +1,28 @@
+package org.jetbrains.jet.codegen.intrinsics;
+
+import com.intellij.psi.PsiElement;
+import org.jetbrains.jet.codegen.ExpressionCodegen;
+import org.jetbrains.jet.codegen.JetTypeMapper;
+import org.jetbrains.jet.codegen.StackValue;
+import org.jetbrains.jet.lang.psi.JetCallExpression;
+import org.jetbrains.jet.lang.psi.JetExpression;
+import org.jetbrains.jet.lang.resolve.BindingContext;
+import org.jetbrains.jet.lang.types.JetType;
+import org.jetbrains.jet.lexer.JetTokens;
+import org.objectweb.asm.Type;
+import org.objectweb.asm.commons.InstructionAdapter;
+
+import java.util.List;
+
+/**
+ * @author alex.tkachman
+ */
+public class StringPlus implements IntrinsicMethod {
+    @Override
+    public StackValue generate(ExpressionCodegen codegen, InstructionAdapter v, Type expectedType, PsiElement element, List<JetExpression> arguments, StackValue receiver) {
+        codegen.gen(arguments.get(0)).put(JetTypeMapper.JL_STRING_TYPE, v);
+        codegen.gen(arguments.get(1)).put(JetTypeMapper.TYPE_OBJECT, v);
+        v.invokestatic("jet/runtime/Intrinsics", "stringPlus", "(Ljava/lang/String;Ljava/lang/Object;)Ljava/lang/String;");
+        return StackValue.onStack(JetTypeMapper.JL_STRING_TYPE);
+    }
+}

compiler/frontend/src/jet/Library.jet

@@ -40,6 +40,8 @@ fun Any?.equals(other : Any?) : Boolean// = this === other
 // Returns "null" for null
 fun Any?.toString() : String// = this === other
 
+fun String?.plus(other: Any?) : String
+
 trait Iterator<out T> {
   fun next()  : T
   val hasNext : Boolean

compiler/tests/org/jetbrains/jet/codegen/FunctionGenTest.java

@@ -26,6 +26,41 @@ public class FunctionGenTest extends CodegenTestCase {
 
     }
 
+    public void testNullableAnyToString () throws InvocationTargetException, IllegalAccessException {
+        loadText("fun foo(x: Any?) = x.toString()");
+        System.out.println(generateToText());
+        Method foo = generateFunction();
+        assertEquals("something", foo.invoke(null, "something"));
+        assertEquals("null", foo.invoke(null, new Object[]{null}));
+
+    }
+
+    public void testNullableStringPlus () throws InvocationTargetException, IllegalAccessException {
+        loadText("fun foo(x: String?, y: Any?) = x + y");
+        String text = generateToText();
+        assertTrue(text.contains(".stringPlus"));
+        System.out.println(text);
+        Method foo = generateFunction();
+        assertEquals("something239", foo.invoke(null, "something", 239));
+        assertEquals("null239", foo.invoke(null, null, 239));
+        assertEquals("239null", foo.invoke(null, "239", null));
+        assertEquals("nullnull", foo.invoke(null, null, null));
+
+    }
+
+    public void testNonNullableStringPlus () throws InvocationTargetException, IllegalAccessException {
+        loadText("fun foo(x: String, y: Any?) = x + y + 120");
+        String text = generateToText();
+        assertFalse(text.contains(".stringPlus"));
+        System.out.println(text);
+        Method foo = generateFunction();
+        assertEquals("something239120", foo.invoke(null, "something", 239));
+        assertEquals("null239120", foo.invoke(null, null, 239));
+        assertEquals("239null120", foo.invoke(null, "239", null));
+        assertEquals("nullnull120", foo.invoke(null, null, null));
+
+    }
+
     public void testAnyEqualsNullable () throws InvocationTargetException, IllegalAccessException {
         loadText("fun foo(x: Any?) = x.equals(\"lala\")");
         System.out.println(generateToText());

stdlib/src/jet/runtime/Intrinsics.java

@@ -0,0 +1,13 @@
+package jet.runtime;
+
+/**
+ * @author alex.tkachman
+ */
+public class Intrinsics {
+    private Intrinsics() {
+    }
+
+    public static String stringPlus(String self, Object other) {
+        return ((self == null) ? "null" : self) + ((other == null) ? "null" : other.toString());
+    }
+}