why no "old" operator in function postconditions, as in Eiffel?

[davidl]

wah, why following my post? looks like a CON-post while it's not :)

Yes, you pointed things out more clearly, "old" keyword as mentioned
only works for the stateless function. And DbC is actually not tho-
roughly or widely viewed carefully enough.

> davidl wrote:
>
>> That feature doesn't worth a keyword at all, and old(blah) pollutes the
>> naming space. You have several choices already:
>>
>> The following shows how your old keyword should work(NOTICE: the code
>> would probably be not compatible with D2.0):
>>
>> int func(int n)
>> out(result)
>> {
>> static int[int] funcmap;      // create a func mapping here for further  
>> old
>> keyword test
>> // while this kind of sanity test would bloat the AA funcmap greatly
>> // But I don't see any other solution without increasing runtime to
>> solve this
>> // problem in *any* other language
>> funcmap[n]=result;
>> if ((n-1) in funcmap)         // test if that has been calculated
>> assert(funcmap[n]==funcmap[n-1]+1);
>> }
>> body
>> {
>> if (n<1) return 0;
>> return func(n-1)+1;
>> }
>> void main()
>> {
>> func(3);
>> }
>>
>
> What is this supposed to solve? DbC is supposed to save the high level
> representation of contracts. Also inheritance as implemented currently
> breaks your example and your function is stateless, so there's absolutely
> no need for 'old' in that.
>
>>> Being a newbie, I already asked in the digitalmars.D.learn ... no one
>>> there knew of a way to do this directly, only with various additional
>>> explicit boilerplate coding by the programmer.
>
> You can always extend the language with metaprogramming. ;)
>
>>> Are there plans to add such support to D?  Searching the archives for
>>> "old" and "Eiffel" and find virtually no mention of this, which amazes
>>> me.  I found "old" to be extremely useful when I coded in Eiffel.  Not
>>> having it in a language that bills itself as supporting DbC seems like
>>> languages which only have "assert" and claim to be supporting DbC.
>
> I hope so. DbC in most languages is a bad joke. They teach you to use  
> @pre
> and @post in javadoc comments in uni these days, but seriously nobody is
> going to use it (correctly) if the compiler cannot enforce anything.  
> That's
> the whole point.



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