this is not an lvalue

[Andrey via Digitalmars-d-learn]

Hello, I'm newbie in D. I'm trying to rewrite my project from C++ 
and now I get strange warning:
src/e2ml/node.d(23,22): Deprecation: this is not an lvalue
As I write the following code
void moveTo(ref Parameter parent) {
    this.p_parent.removeValue(this);
    this.p_parent = parent;
    this.updatePath();
}

How to fix it?