Re: is LISP the ultimate prgram language?
On Oct 21, 3:51 pm, Keith H Duggar <dug...@alum.mit.edu> wrote:
On Oct 21, 4:22 am, James Kanze <james.ka...@gmail.com> wrote:
On Oct 20, 8:19 pm, Juha Nieminen <nos...@thanks.invalid> wrote:
If you have, for example, a vector of ints, where each int
is a full-fledged object (in other words, some of the ints
could actually be objects derived from an int), then I
don't think the compiler has any way of optimizing dynamic
binding checks away. It cannot prove that none of the ints
in the array are objects derived from int.
It can, and some do. Obviously, it's harder for the
compiler than optimizing around std::vector, but then,
optimizing around std::vector is harder for the compiler
than optimizing around Fortran style arrays. (C-style
arrays are a problem for the compiler, because they end up
being pointers.)
And what would you replace this C-style array "problem" with?
Make arrays first class types, behaving as any other type.
In other words, how would you implement iterators for C-style
array sequences?
The same way you implement them for any other container. For
that matter, you usually inhibit the convertion of array to
pointer (by using pass by reference) when you want "iterators"
for C style arrays, using something like:
template< typename T, size_t n >
T*
end( T (&array)[ n ] )
{
return array + n ;
// or return &array[0] + n, if there was no conversion,
// or just something like
// return array.end(), if the language were defined
// thusly.
}
Basically, you block the conversion because it involves loss of
important information concerning the type, mainly how many
elements the array contains.
Do you have a link to a proposal for C++ or examples of
languages that "do it right" and support Stepanov iterator
concepts as C++ does?
The STL has been implemented in Ada. The problems doing so had
nothing to do with arrays; the problems had to do with the fact
that Ada's generics work somewhat differently than those in C++.
And of course, one might reasonably ask why you would want to
use the STL iterator idiom, which follows the C idiom in
requiring a separate object to contain all of the necessary
information, when you could put all the information in a single
object, resulting in a more powerful and simpler to use
abstraction.
--
James Kanze