Bug 24034 – Changing this in constructor allows to modify immutable members of other instance

Pull request https://github.com/dlang/dmd/pull/15389 for issue 24024 allows to modify `this` for classes inside functions. In constructors this allows to modify immutable members of another instance of the same class. The constructor will now also return the wrong pointer. import std.stdio; class C { immutable int i; this(int i, C other) { if (other !is null) this = other; this.i = i; } } void main() { C c1 = new C(1, null); writeln(c1.i); // prints 1 C c2 = new C(2, c1); writeln(c1.i); // prints 2 writeln(c2.i); // prints 2 writeln(c1 is c2); // prints true }

Yeah, this is bad. I guess `this` should not be modifiable for classes when used in constructors. For normal functions it could be allowed.

The pull for issue 24024 was reverted and it was marked WONTFIX. Assignment to `this` now gives: thislval2.d(8): Error: cannot modify expression `this` because it is not an lvalue