Fully dynamic d by opDotExp overloading

[davidl]

在 Fri, 17 Apr 2009 22:24:04 +0800，Steven Schveighoffer  
<schveiguy at yahoo.com> 写道:

> 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.
>

The opDotExp overload func is supposed to deal with that, because it's in  
your hand to deal with the dynamic properties. The example here is  
illustrating the 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
> }
>

The problem is you're dealing with the class which is overloaded its  
opDot. You know the risk before hand, you are not going to overload for  
every classes. Here, you seem to little bit overrate this feature. :)
If you want things checked, then you probabely need to go back to static.  
This dynamic stuff is used for dynamic things only, and as long as you  
have to do it in the dynamic way that means you have no easy way or even  
impossible to check it at compiletime and you accept the potential risk  
like the example you posted.

> Also, how do you overload the return value?  Using this proposal, you  
> can't have different dynamic methods that return different types.
>

Umm, maybe make the compiler to pass the return type into the opDot would  
allow the opDot func to decide which overload func to call.

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