scala case class copy implementation

Question

I can't find how copy is implemented for case class in scala.

Can I check it somehow?

I though Intellij could point me to implementation, but it doesn't want to jump and I have no idea why :/

It is generated by scalac, it would look something like this http://stackoverflow.com/a/6637597/5123895 To actually see it I think you would need to compile and decompile or enable some option in scalac. — Łukasz, Feb 25 '16 at 12:03

Yuval Itzchakov · Accepted Answer · 2016-02-25T13:59:59.753

4

You can inspect the scala case class output using scalac -print ClassName.scala, as the copy is actually a compiler generated method.

Here's a given example:

case class Test(s: String, i: Int)

This is the output after filtering out noise for copy:

case class Test extends Object with Product with Serializable {
    private[this] val s: String = _;
    def s(): String = Test.this.s;

    private[this] val i: Int = _;
    def i(): Int = Test.this.i;

    def copy(s: String, i: Int): common.Test = new common.Test(s, i);
    def copy$default$1(): String = Test.this.s();
    def copy$default$2(): Int = Test.this.i();
}

edited Feb 25 '16 at 13:59

answered Feb 25 '16 at 13:45

Yuval Itzchakov

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This is a little weird with copy$default$1 and copy$default$2. I am still not sure what will be called when I would do `Test("a",3).copy(i=5)` – kpbochenek Feb 25 '16 at 20:50
This is what gets called: `def copy(s: String, i: Int): common.Test = new common.Test(s, i);` – Yuval Itzchakov Feb 26 '16 at 08:40
Okay so it calls some methods of classes we don't see :-)) most acutely, does it avoid reflection? – matanster Jul 05 '18 at 11:54
2

@matanster Yes, it is compile time generated. – Yuval Itzchakov Jul 05 '18 at 11:57

scala case class copy implementation

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