Generic const - a non-functional view

[Steven Schveighoffer]

"Jason House" wrote
> Steven Schveighoffer wrote:
>> I would really like to hear people's opinions, especially Walter's.
>
> What I like:
> * Sticking to fundamental principles
> * The const!(A,B)(T) syntax looks quite clean
> * The ability for mixed const (AKA restricted mutability)
>
> What I don't like:
> * const!(~mutable)(T) syntax.  While a mutable keyword may be kind of 
> nice,
> the syntax is starting to get clunky and also become the only syntax
> for "not const"

Yes, it is clunky, but also hidden :)  All you ever have to do is use 
'mutable', 'lconst', and 'linvariant.'  Compare it to mixins or templates.

import std.mutable;

class myclass
{
   mutable int x;
   int y;
}

void f(lconst(myclass) input)
{
    input.y = 2; // error, input.y is const
    input.x = 3; // ok.
}

> * No discussion of how to define const/invariant functions

I did leave this out.  Since const!(T) is analogous to const, it would be 
the same:

class myclass
{
   lconst void f() { /* 'this' is lconst */}
   void f2() lconst {/* same thing */}
}

> A lot of times, when I think about tail const/mixed const/mutable/..., I
> start thinking about arrays.
> AKA:
>  T[] vs. array!(T)
>  const(T)[] vs. array!(const(T)) vs. const!(element)(array!(T))

or const!(element)(T)[]

or

alias const!(element) eleconst;

eleconst(T)[]

-Steve