an old topic (pun intended)

[kennytm]

Davidson Corry <davidsoncorry at comcast.net> wrote:
> On 10/27/2011 2:12 PM, Timon Gehr wrote:
>> Yes, this design has indeed a keyword-issue that your proposal has not.
>> I am all for not making it a keyword. The 'body' keyword imho should be
>> removed too, there is only one place in the grammar where it is ever
>> needed (and there it is completely redundant), therefore it could just
>> be lexed as an identifier. That would not break any code.
> 
> Agreed. In fact, it occurred to me the other day that we could write contracts as
> 
>     void foo(T t)
>     {
>         scope(in) {
>              // pre-condition contracts
>         }
>         scope(out) {
>              // post-condition contracts
>         }
>         // ...body of function...
>     }
> 
> and eliminate the 'in', 'out' and 'body' keywords/constructs entirely.
> 
> Similarly, an invariant could appear in the default constructor of a class as
> 
>     this()
>     {
>         scope(invariant) {
>             // invariant guarantees...
>         }
>         // ...body of constructor...
>     }
> 
> Or *any* constructor, really, although you would probably want the
> compiler to enforce that no more than one constructor defined a
> scope(invariant) block. This notation also suggests (correctly) that the
> invariant doesn't take effect until you have entered the constructor.
> (Exited it, really, but...)
> 
> -- Davidson

The contracts are parts of the function's interface, not implementation. If
you put the scope(in/out) inside the '{ ... }' how would a .di file handle
it?

And class invariant is also checked outside the constructor. Your syntax
makes it look like it will run only when the constructor is called.