From slices to perfect imitators: opByValue

[monarch_dodra via Digitalmars-d]

On Thursday, 8 May 2014 at 12:48:17 UTC, Sönke Ludwig wrote:
> Am 08.05.2014 13:05, schrieb monarch_dodra:
>> Not necessarily: As soon as indirections come into play, you 
>> are
>> basically screwed, since const is "turtles all the way down".
>>
>> So for example, the conversion from "const RefCounted!T" to
>> "RefCounted!(const T)" is simply not possible, because it 
>> strips the
>> const-ness of the ref count.
>>
>> What we would *really* need here is NOT:
>> "const RefCounted!T" => "RefCounted!(const T)"
>> But rather
>> "RefCounted!T" => "RefCounted!(const T)"
>>
>> The idea is to cut out the "head const" directly. This also 
>> applies to
>> most ranges too BTW.
>>
>> We'd be much better of if we never used `const MyRange!T` to 
>> begin with,
>> but simply had a conversion from `MyRange!T` to 
>> `MyRange!(const T)`,
>> which references the same data.
>>
>> In fact, I'm wondering if this might not be a more interesting 
>> direction
>> to explore.
>
> The reference count _must_ be handled separate from the 
> payload's const-ness, or a const(RefCount!T) would be 
> completely dysfunctional.

Right, which is my point: "const(RefCount!T)" *is* dysfunctional, 
which is why you'd want to skip it out entirely in the first 
place.This holds true for types implemented with RefCount, such 
as Array and Array.Range.