Hello guys. Imaging you have a big data class `Pro...

# compiler

[Artyom Gornostayev]

Hello guys.
Imaging you have a big data class Product with a log of attributes (nullable and non-nullable).
Compiler generates byte code where it creates constructor similar to this:
Product.decompiled.java

...
   // $FF: synthetic method
   public Product(String var1, ..., int var40, int var41, DefaultConstructorMarker var42) {
      if ((var40 & 1073741824) != 0) {
         var31 = null;
      }

      if ((var40 & Integer.MIN_VALUE) != 0) {
         var32 = null;
      }

      if ((var41 & 1) != 0) {
         var33 = null;
      }

      if ((var41 & 2) != 0) {
         var34 = null;
      }

      ...

      this(var1, ... var39);
   }

There are two attributes var40 and var41 which (as I understood) rules nullability...
What is a logic behind this? Why compiler splits nullable fields into two groups?
Thanks a lot.

[dmitriy.novozhilov]

This constructor is generated because you have default values for some of those parameters
var40 and var41 are bit masks which determine what values were passed explicitly and what should be taken from default

It seems like all your defaults are null, so you can see varXX = null
Check the other case:

data class Some(val x: String = "a", val y: String? = null)

// decompiled
   public Some(String var1, String var2, int var3, DefaultConstructorMarker var4) {
      if ((var3 & 1) != 0) {
         var1 = "a";
      }

      if ((var3 & 2) != 0) {
         var2 = null;
      }

      this(var1, var2);
   }

Note that in this example there is only one int parameter, because Some constructor has less than 32 parameters, and it's enough just one int to cover all cases

[Artyom Gornostayev]

Thanks a lot for a quick response.