Some work for string concatenation. (#40)

runtime/src/main/cpp/Natives.cpp

@@ -226,4 +226,10 @@ KInt Kotlin_String_hashCode(const ArrayHeader* thiz) {
   return CityHash64(ByteArrayAddressOfElementAt(thiz, 0), thiz->count_);
 }
 
+KRef Kotlin_String_subSequence(
+    const ArrayHeader* thiz, KInt startIndex, KInt endIndex) {
+  RuntimeAssert(false, "Unsupported operation");
+  return nullptr;
 }
+
+}  // extern "C"

runtime/src/main/cpp/Natives.h

@@ -91,6 +91,8 @@ ArrayHeader* Kotlin_String_fromUtf8Array(const ArrayHeader* array);
 ArrayHeader* Kotlin_String_plusImpl(
     const ArrayHeader* thiz, const ArrayHeader* other);
 KInt Kotlin_String_getStringLength(const ArrayHeader* thiz);
+KRef Kotlin_String_subSequence(
+    const ArrayHeader* thiz, KInt startIndex, KInt endIndex);
 
 #ifdef __cplusplus
 }

runtime/src/main/kotlin/kotlin/Any.kt

@@ -2,8 +2,8 @@ package kotlin
 
 @ExportTypeInfo("theAnyTypeInfo")
 public open class Any {
-    // @SymbolName("Kotlin_Any_equals")
-    // external public open operator fun equals0(other: Any0?): Boolean
+    @SymbolName("Kotlin_Any_equals")
+    external public open operator fun equals(other: Any?): Boolean
 
     // TODO: do we need that in Any?
     @SymbolName("Kotlin_Any_hashCode")

runtime/src/main/kotlin/kotlin/CharSequence.kt

@@ -0,0 +1,25 @@
+package kotlin
+
+/**
+ * Represents a readable sequence of [Char] values.
+ */
+public interface CharSequence {
+    /**
+     * Returns the length of this character sequence.
+     */
+    public val length: Int
+
+    /**
+     * Returns the character at the specified [index] in this character sequence.
+     */
+    public operator fun get(index: Int): Char
+
+    /**
+     * Returns a new character sequence that is a subsequence of this character sequence,
+     * starting at the specified [startIndex] and ending right before the specified [endIndex].
+     *
+     * @param startIndex the start index (inclusive).
+     * @param endIndex the end index (exclusive).
+     */
+    public fun subSequence(startIndex: Int, endIndex: Int): CharSequence
+}

runtime/src/main/kotlin/kotlin/String.kt

@@ -4,27 +4,32 @@ package kotlin
 external fun fromUtf8Array(array: ByteArray) : String
 
 @ExportTypeInfo("theStringTypeInfo")
-class String {
+class String : Comparable<String>/* , CharSequence */ {
     @SymbolName("Kotlin_String_hashCode")
     external public override fun hashCode(): Int
 
-/* TODO: calling to virtual method (plusImpl) results in link error; uncomment after supporting
-calling virtual methods in translator
-    public operator fun plus(other: Any?): String {
+    // TODO: make it Any?
+    public operator fun plus(other: Any): String {
         return plusImpl(other.toString())
     }
-*/
 
-    public val length: Int
+    /*
+    public fun override toString(): String {
+        return this
+    } */
+
+    public /* override */ val length: Int
         get() = getStringLength()
 
     // Can be O(N).
     @SymbolName("Kotlin_String_get")
-    external public fun get(index: Int): Char
+    external /* override */ public fun get(index: Int): Char
+
+    @SymbolName("Kotlin_String_subSequence")
+    external /* override */ public fun subSequence(startIndex: Int, endIndex: Int): CharSequence
 
-    // external public fun subSequence(startIndex: Int, endIndex: Int): CharSequence
     @SymbolName("Kotlin_String_compareTo")
-    external public fun compareTo(other: String): Int
+    override external public fun compareTo(other: String): Int
 
     @SymbolName("Kotlin_String_getStringLength")
     external private fun getStringLength(): Int
@@ -33,5 +38,5 @@ calling virtual methods in translator
     external private fun plusImpl(other:Any): String
 
     @SymbolName("Kotlin_String_equals")
-    external public override operator fun equals(other: Any?): Boolean
+    external public override fun equals(other: Any?): Boolean
 }

runtime/src/main/kotlin/kotlin/Unit.kt

@@ -1,5 +1,5 @@
 package kotlin
 
 public object Unit {
-    // override fun toString() = "kotlin.Unit"
+    override fun toString() = "kotlin.Unit"
 }