Fully dynamic d by opDotExp overloading

[Denis Koroskin]

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?