preparing for const, final, and invariant

[Chris Nicholson-Sauls]

Walter Bright wrote:
> This is coming for the D 2.0 beta, and it will need some source code 
> changes. Specifically, for function parameters that are arrays or 
> pointers, start using 'in' for them.
> 
> 'in' will mean 'scope const final', which means:
> 
> final - the parameter will not be reassigned within the function
> const - the function will not attempt to change the contents of what is 
> referred to
> scope - the function will not keep a reference to the parameter's data 
> that will persist beyond the scope of the function
> 
> For example:
> 
> int[] g;
> 
> void foo(in int[] a)
> {
>     a = [1,2];    // error, a is final
>     a[1] = 2;   // error, a is const
>     g = a;    // error, a is scope
> }
> 
> Do not use 'in' if you wish to do any of these operations on a 
> parameter. Using 'in' has no useful effect on D 1.0 code, so it'll be 
> backwards compatible.
> 
> Adding in all those 'in's is tedious, as I'm finding out :-(, but I 
> think the results will be worth the effort.

Sounds good to me.  How soon can we expect 2.0beta?

-- Chris Nicholson-Sauls