const sucks

[John Reimer]

Hello Walter,

> Bill Baxter wrote:
> 
>> I think you mean "this option is being discussed *once again*".  It
>> was discussed quite a lot before the current invariant/const was
>> implemented.  The consensus was definitely that it was worth a shot.
>> But it did not get a shot.
>> 
> Yes, it was discussed a lot.
> 
>> I recall Walter's main argument against it was that local variable
>> really shouldn't be const-by-default since you're usually creating
>> them because you want to manipulate them.  But then you end up with a
>> system where local variable declarations and parameter declarations
>> follow very different rules.  "int[] foo" in one place means
>> something different from "int[] foo" in the other place.  I'm not
>> convinced this would be that confusing, though.  There could be other
>> problems with const-by-default in parameters, but that one doesn't
>> seem like such a big deal.
>> 
> The problem is things like:
> 
> void foo(int[] a)
> {
> int[] b;
> }
> so a is const, and b is mutable? That's very confusing. It gives the
> appearance of D having a lot of wacky and arbitrary semantic rules.
> 


I'll have to go dig up all the past discussions on this (there were volumes 
that I mostly skipped over).

My impression of mutable by default was more than function parameters.

Weren't we talking something like this when referring to "immutable by default":

// void foo(int[] a)
// {
//     int b;
//     mutable int c;
//
//     /* block declaration */
//
//     mutable 
//     {
//          int d;
//          int e;
//      }
// }

'a' is an implied const (immutable) parameter.
'b' is const by default
'c', 'd', and 'e' are all declared mutable.

Isn't this what is meant by "constant by default"?  I haven't described class 
variables here, of course.

I'm nervous to comment further lest I have totally misunderstood what's going 
on. :)

-JJR