Hi Eliot,Le 19 mars 2014 � 16:25, Eliot Miranda a �crit :ok, I understand. Thank you for the explanation.Hi�Christophe,Le 18 mars 2014 � 19:50, Eliot Miranda a �crit :On Tue, Mar 18, 2014 at 10:10 AM, Christophe Demarey <Christophe.Demarey@inria.fr> wrote:
Why arguments should be read only?They are just temporary variables with an initial value.Read the blue book. �It was a decision of the language designers to forbid assignment to arguments to allow debugging. �The assignment to block arguments is a side-effect of the old BlockContext implementation of blocks where block arguments were mapped onto temporary variables of the home context. �It is an anachronism and should be forbidden also.Thank you for the explanation.I'm just curious why it is so difficult to implement a debugger if arguments are assignable?If you need to restart the execution of a method, and so you need to get the initial value of the argument, I understand you cannot find the value anymore in the method context but it is available in the caller context, no?As I never implemented a debugger, I cannot figure out the difficulties.the args are no longer available; they get moved from the caller context to the callee. �If you think about stack frames then what happens is that the slots containing the outgoing arguments are used as the slots for the�incoming arguments. �So if arguments are assigned to they are indeed lost.But look at how many methods in the system (or in any system). �The proportion of methods/functions/procedures that could be written to assign their arguments is very small so the Smalltalk trade off is a good one.
I agree we don't really loose something. You can always assign arguments to temporary variables and update temporary variables. My point was just: if possible, why don't do it?