This(KeyWord)

The 'this' is a keyword that refers to the this parameter.

It is a address that points to the object of the class of which the member function is called.

$Item:
   int Hp;
     
   |DoDamage[this&]:
    this.Hp = 10;
   
    Hp = 10;//does the same as above

    int V = this.Hp;
    
    int V2 = this.Hp;//does the same as above

The this keyword can also be used to be an alias current class type.

$BigTree:
  int Hp;
  |AddBoth[umut this&,umut this& Other] -> BigTree:
     ret [this.Hp + Other.Hp];

becomes

  $BigTree:
    int Hp;
    |AddBoth[umut BigTree,umut BigTree& Other] -> Item:
     ret [this.Hp + Other.Hp];