Re: Lower bounds of Strings

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

"Stephen Davies" <joviangm@gmail.com> wrote in message 
news:1ea70290-a1a8-4a63-8f38-922e966084c9n@googlegroups.com...
> On Friday, 15 January 2021 at 17:35:54 UTC, Stephen Davies wrote:
>> On Friday, 15 January 2021 at 11:41:24 UTC, J-P. Rosen wrote:
>> > function Slide (S : String) return String is
>> > (S(S'First) & S (S'First+1 .. S'Last));
>> To me, this is a fundamental enough operation that, in the absence of
>> being able to specify a subtype where it happens automatically, it at
>> least deserves to be an attribute.
> Also, a Slide function does not work for "out" and "in out" parameters.
> Admittedly, ehh.p...'s workaround does solve this, but I would prefer
> a proper solution in the language, e.g. a Slide attribute that acts as a
> view conversion.

Thank god. Slices passed as in out parameters are the bane of the 
compiler-writers existence, and outside of types like String, have a very 
expensive implementation. On common machines like the x86, copying an 
arbitrary bit string from one location to another is not an easy operation 
to perform. (Remember, one can slice packed arrays, arrays of controlled 
objects, and other nasty cases. And with the sort of interface others here 
are proposing, you'd have to do it for various discontiguous 
representations, too.)

This way leads to madness -- at least of compiler implementers. ;-)

                             Randy.