Re: ADA.STRINGS.INDEX_ERROR : a-strunb.adb:782

[AdaMagica <christ-usch.grein@t-online.de>]

Am Donnerstag, 18. Januar 2018 09:34:51 UTC+1 schrieb Dmitry A. Kazakov:
> You can rename result of a function too. (It does make much sense in the 
> case of scalar values returned by value).
> 
> However you cannot rename a non-object. A subtle distinction, but it is 
> there. That would prevent renaming of an attribute Object'Length which 
> is not an object for whatever strange reason.

Simple. Attribute Length is universam_integer.

> Attributes have a long 
> history of being queer. E.g. "abc"'Length is still illegal, AFAIK. In 
> Ada attributes are not considered operations as they should.

Back to Ada 80/83:

A requirement on all predefinied operations on scalar types was that they could not be hidden - so they had to be operators. Ada 80 had Abs as a function name, which was accordingly changed to "abs".
So everything else had to use some other syntax - this was chosen to be attributes.

And since Length has no relation to the index type, but had to be usable for any integer type, the solution was universal_integer, as was also chosen for some others.

And of course are attributes operations (see RM, for instance 3.5.5) - they are not operators!