Re: Lower bounds of Strings

["Randy Brukardt" <randy@rrsoftware.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:rtaeok$l8b$1@gioia.aioe.org...
> On 2021-01-08 18:23, Shark8 wrote:
>> On Thursday, January 7, 2021 at 3:03:54 PM UTC-7, Randy Brukardt wrote:
>
>>> Any sort of multiple inheritance (not to mention multiple dispatch) 
>>> requires
>>> searching a lookup table for the appropriate interface.
>> Ah.
>> It appears you're confusing the Ada concept underlying keyword INTERFACE 
>> with the general/abstract notion.
>> It appears to me that Dmitry is referring to the latter, not the 
>> Ada-construct of INTERFACE, which requires a tagged type.
>>
>> I think what he's getting at is something that I considered/proposed here 
>> on C.L.A some years ago, adding the concept of an "ABSTRACT INTERFACE" to 
>> Ada. (IIRC, the proposal I had in mind was to be able to model the 
>> notional meta type-hierarchy; eg: Number ? Universal_Integer ? 
>> System.Integer.)
>
> Right, though I do not think that tags can inflict any cost. The situation 
> is same as with array bounds. You do keep bounds when the array is 
> statically constrained. Tag is just another constraint like bounds. It 
> must be handled just same way, removed when statically known. No penalty, 
> unless classes are actually used. I do not know why people always bring 
> dispatch into discussions about static cases.

The possibility of dynamic dispatch (in some code that doesn't exist yet, 
but *could*) is what is so expensive and is virtually impossible to remove 
after the fact (that is, in an optimizer). If you wanted to include a 
declaration that you *never* were going to use any dynamic dispatch, then 
you could talk try to ignore the possibility. But without some sort of 
dispatch, a defined interface buys you nothing other than complication. It 
doesn't simplify the description and would substantially complicate the 
implementation. What's the point??

                              Randy.