byKey and byValue: properties or methods?

[Steven Schveighoffer]

On Wed, 18 Jan 2012 08:59:57 -0500, Andrei Alexandrescu  
<SeeWebsiteForEmail at erdani.org> wrote:

> On 1/18/12 7:20 AM, Steven Schveighoffer wrote:
>> The only array-specific properties of an array that the compiler should
>> worry about are ptr and length. Everything else should be a library
>> function.
>
> Even ptr and length should be in the library. The slice structure should  
> be defined in object.d. The only business the compiler has is to lower  
> the T[] type syntax and the [ ... ] literal syntax to .object.Slice!T  
> and .object.slice(...) form, and to make sure that typeof(T[]) is not  
> struct (although factually it is).

That is debatable.  The exact semantics of length are not repeatable in  
the library, where a get is a simple field access, yet a set calls a  
method.  To achieve the same you would have to require -inline on the  
compile line.

At that point, we have to say "what does it buy us".  The function to set  
the length is already a library function, which is changable outside the  
compiler.  What do we gain besides saying the language is purer?

If we change dup and idup to be library defined, we can get benefits, such  
as taking advantage of pure being able to implicitly cast to immutable.

-Steve