Fully dynamic d by opDotExp overloading

[Andrei Alexandrescu]

Denis Koroskin wrote:
> On Fri, 17 Apr 2009 18:24:04 +0400, Steven Schveighoffer <schveiguy at yahoo.com> wrote:
> 
>> On Fri, 17 Apr 2009 09:44:09 -0400, Leandro Lucarella <llucax at gmail.com>  
>> wrote:
>>
>>> I don't fully understand the example though. In writefln((v.qq = 5).i),
>>> how is that B.i is assigned to 5 if the opDotExp("qq", 5) don't  
>>> propagate
>>> the 5 to the new B()?
>> I think it translates to
>>
>> opDotExp("qq") = 5
>>
>> Without knowing the signature of qq, how is the compiler supposed to  
>> infer that it is a property?  In fact, I think this might be a  
>> limitation of this syntax, you can't define dynamic properties.
>>
>> I for one, can't really see a huge benefit, but then again, I don't  
>> normally work with dynamic-type langauges.  It looks to me like a huge  
>> hole that the compiler will ignore bugs that would have been caught if  
>> the methods were strongly typed:
>>
>> class c
>> {
>>    void opDotExp(char[] methodname,...)
>>    {
>>       if(methodname == "mymethod")
>>          callMyMethod();
>>       else
>>          throw new Exception("bad method name: " ~ methodname);
>>    }
>> }
>>
>> void foo(c myc, bool rarelySetToTrue)
>> {
>>    if(rarelySetToTrue)
>>      myc.mymethud(); // compiles, will throw runtime exception
>> }
>>
>> Also, how do you overload the return value?  Using this proposal, you  
>> can't have different dynamic methods that return different types.
>>
>> -Steve
> 
> Here is how it could be done:
> 
> class C
> {
>     auto opDot(string methodName, T... args)(T args) // opDotExp renamed to opDot
>     {
>         static if (methodName == "length") {
>             return _length; // return type is size_t
>         } else static if (methodName == "resize") {
>             _resize(args); // return type is void
>         }
>     }
> }
> 
> This is a great use-case for compile-time "static switch". Can we haz one, please?

I think the more urgent need is for static loops. At least we have a 
simple workaround for static switch.

Andrei