testing kotlin string concatenation bytecode results

kot-strings-bytecode

fun test() {
    val x = "a" + "b" + "c"
}

fun test2() {
    val sb = StringBuilder()
    sb.append("a").append("b").append("c")
    val x = sb.toString()
}

fun test3() {
    val a = "a"
    val b = "b"
    val c = "c"
    val x = "$a $b $c"
}

////////////////// bytecode

public final static test()V
   L0
   L1
   L2
   L3
    LINENUMBER 63 L3
    NEW java/lang/StringBuilder
    DUP
    INVOKESPECIAL java/lang/StringBuilder.<init> ()V
    LDC "a"
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
    LDC "b"
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
    LDC "c"
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
    INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String;
    ASTORE 0
   L4
    LOCALVARIABLE x Ljava/lang/String; L2 L4 0
    RETURN
   L5
    MAXSTACK = -1
    MAXLOCALS = -1

  // access flags 0x19
  public final static test2()V
   L0
   L1
   L2
   L3
    LINENUMBER 67 L3
    NEW java/lang/StringBuilder
    DUP
    INVOKESPECIAL java/lang/StringBuilder.<init> ()V
    ASTORE 0
   L4
    LINENUMBER 68 L4
    ALOAD 0
    LDC "a"
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
    DUP
    LDC "StringBuilder"
    LDC "append"
    INVOKESTATIC kotlin/jvm/internal/Intrinsics.checkReturnedValueIsNotNull (Ljava/lang/Object;Ljava/lang/String;Ljava/lang/String;)V
    LDC "b"
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
    DUP
    LDC "StringBuilder"
    LDC "append"
    INVOKESTATIC kotlin/jvm/internal/Intrinsics.checkReturnedValueIsNotNull (Ljava/lang/Object;Ljava/lang/String;Ljava/lang/String;)V
    LDC "c"
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
    DUP
    LDC "StringBuilder"
    LDC "append"
    INVOKESTATIC kotlin/jvm/internal/Intrinsics.checkReturnedValueIsNotNull (Ljava/lang/Object;Ljava/lang/String;Ljava/lang/String;)V
    POP
   L5
   L6
    LINENUMBER 69 L6
    ALOAD 0
    INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String;
    DUP
    LDC "StringBuilder"
    LDC "toString"
    INVOKESTATIC kotlin/jvm/internal/Intrinsics.checkReturnedValueIsNotNull (Ljava/lang/Object;Ljava/lang/String;Ljava/lang/String;)V
    ASTORE 1
   L7
    LOCALVARIABLE x Ljava/lang/String; L5 L7 1
    LOCALVARIABLE sb Ljava/lang/StringBuilder; L2 L7 0
    RETURN
   L8
    MAXSTACK = -1
    MAXLOCALS = -1

  // access flags 0x19
  public final static test3()V
   L0
   L1
   L2
   L3
    LINENUMBER 73 L3
    LDC "a"
    ASTORE 0
   L4
   L5
    LINENUMBER 74 L5
    LDC "b"
    ASTORE 1
   L6
   L7
    LINENUMBER 75 L7
    LDC "c"
    ASTORE 2
   L8
   L9
    LINENUMBER 76 L9
    NEW java/lang/StringBuilder
    DUP
    INVOKESPECIAL java/lang/StringBuilder.<init> ()V
    ALOAD 0
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
    LDC " "
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
    ALOAD 1
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
    LDC " "
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
    ALOAD 2
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
    INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String;
    ASTORE 3
   L10
    LOCALVARIABLE x Ljava/lang/String; L8 L10 3
    LOCALVARIABLE c Ljava/lang/String; L6 L10 2
    LOCALVARIABLE b Ljava/lang/String; L4 L10 1
    LOCALVARIABLE a Ljava/lang/String; L2 L10 0
    RETURN
   L11
    MAXSTACK = -1
    MAXLOCALS = -1