an old topic (pun intended)

[Davidson Corry]

On 10/27/2011 9:04 PM, bearophile wrote:
>> >  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...
>> >        }
 >
> How do you replace out(result) with scope(out) {} ?

I am not sure that we need to. D2 has two forms of the 'out()' statement 
now: 'out(result)' and 'out(...)' [as it is shown in the DPL book, or 
just 'out' in current practice].

The only reason to have an 'out(result)' form is to declare that we 
intend to use the magic 'result' symbol in the post-condition testing. 
Does this mean that, if we *don't* pre-declare 'out(result)' that the 
symbol 'result' can have some *other* meaning in the post-condition?

That strikes me as a source of subtle bugs, if a programmer might 
accidentally fail to declare 'out(result)' and thereby get different 
semantics in the post-condition code without having changed that code.

I think the thing to do is to just declare 'out' as we currently do [or 
'scope(out)' as I am proposing], and treat the 'result' symbol magically 
in the post-condition code whether or not it is pre-declared -- that is, 
have the compiler find it and interpret it as the magic returned-value.

-- Davidson