The error I get from the compiler is "The left hand side of an assignment must be a variable". My use case is deep copying, but is not really relevant.
In C++, one can assign to *this.
The question is not how to circumvent assignment to this. It's very simple, but rather what rationale is there behind the decision not to make this a variable.
Are the reasons technical or conceptual?
My guess so far - the possibility of rebuilding an Object in a random method is error-prone (conceptual), but technically possible.
Please restrain from variations of "because java specs say so". I would like to know the reason for the decision.
In C++, one can assign to
*this
Yes, but you can't do this = something in C++, which I actually believe is a closer match for what you're asking about on the Java side here.
[...] what rationale is there behind the decision not to make
thisa variable.
I would say clarity / readability.
this was chosen to be a reserved word, probably since it's not passed as an explicit argument to a method. Using it as an ordinary parameter and being able to reassign a new value to it, would mess up readability severely.
In fact, many people argue that you shouldn't change argument-variables at all, for this very reason.
Are the reasons technical or conceptual?
Mostly conceptual I would presume. A few technical quirks would arise though. If you could reassign a value to this, you could completely hide instance variables behind local variables for example.
My guess so far - the possibility of rebuilding an Object in a random method is error-prone (conceptual), but technically possible.
I'm not sure I understand this statement fully, but yes, error prone is probably the primary reason behind the decision to make it a keyword and not a variable.