OT (partially): about promotion of integers

[bearophile]

Walter Bright:

> Why stop at 64 bits? Why not make there only be one integral 
> type, and it is of whatever precision is necessary to hold the 
> value? This is quite doable, and has been done.

I think no one has asked for *bignums on default* in this thread.


> But at a terrible performance cost.

Nope, this is a significant fallacy of yours.
Common lisp (and OCaML) uses tagged integers on default, and they 
are very far from being "terrible". Tagged integers cause no heap 
allocations if they aren't large. Also the Common Lisp compiler 
in various situations is able to infer an integer can't be too 
much large, replacing it with some fixnum. And it's easy to add 
annotations in critical spots to ask the Common Lisp compiler to 
use a fixnum, to squeeze out all the performance.
The result is code that's quick, for most situations. But it's 
more often correct. In D you drive with eyes shut; sometimes for 
me it's hard to know if some integral overflow has occurred in a 
long computation.


> And, yes, in D you can create your own "BigInt" datatype which 
> exhibits this behavior.

Currently D bigints don't have short int optimization. And even 
when this library problem is removed, I think the compiler 
doesn't perform on BigInts the optimizations it does on ints, 
because it doesn't know about bigint properties.

Bye,
bearophile